WATER
GENERAL CONSIDERATIONS
Necessity for Proper Supply
One of the most important requisites in maintaining the organization
of the material in the living body is a proper supply of water. It is
absolutely indispensable to the expression of animal and vegetable
life. Although not classed as a food it enters into the composition
of food and hence becomes an essential article of diet.
The greatest value has always been placed upon a sufficient supply
of pure water. The history of the race shows that the earliest
settlements were made with a view to obtaining a supply of water;
they were either on waterways or in places where water was easily
obtainable from springs or shallow wells.
Water is needed not only as an article of diet, but it is also
required for sanitary purposes: for cleansing the body externally,
for washing clothes, and also for sprinkling streets and for other
purposes such as sewage disposal in the thickly populated centers.
Even in ancient times great sums of money were expended for the
public supply of water.
History of Public Water Supply
A bit of history on this subject might be of interest to some. It is
asserted by historians that there are aqueducts in China dating back
to prehistoric times. Channels cut in solid rock have been revealed
in Jerusalem in recent excavation which indicate that they were
used for conveying the water supply from the country near Bethlehem
and Hebron. There have been found in these excavations channels of
earthen pipes cemented together and covered with rough rocks. The
fact is also quite well established that water was brought to Athens
from Mount Hymettos and Mount Pentelikon.
As early as 312 B. C. water was carried to Rome through an aqueduct
ten miles long. It is estimated that the cost of construction of
this aqueduct was about $12,700,000. Another was begun in 272 B. C.,
the length of which was forty-five miles. The water carried by this
aqueduct was not used for drinking but for irrigating purposes and
for flushing drains.
Altogether there were at least nine aqueducts that supplied the
ancient city of Rome. Of these nine, three are still used to supply
modern Rome. One of these was finished by Agrippa in 27 B. C.
We see by the foregoing that from time immemorial there has been a
great expenditure of energy and money in producing a proper water
supply for the human family. It also reveals the fact that the
ancients knew something about engineering projects which some of us
are likely to consider as modern accomplishments.
Composition of Water
Water is not, as was previously supposed, an elementary substance.
In 1781 it was shown by Cavendish that it consisted of two parts of
hydrogen and one part of oxygen (H_{2}O), and that it could be made
synthetically by combining hydrogen and oxygen in this proportion,
and that it could be separated analytically by various methods into
its component parts.
By volume, water is composed of two parts of hydrogen to one part of
oxygen; by weight, one part of hydrogen to eight parts of oxygen.
However, pure water does not exist in Nature since water is a
universal solvent and in Nature it comes in contact with so many
substances; therefore, it contains many substances in solution.
Chemically pure water is found only in the chemist’s flask.
Water is a liquid which is clear, colorless and odorless. To be
palatable it should be cool, soft, well aerated and free from
sediment and suspended impurities. One cannot judge the purity of
water by any one of these qualities, for water that is palatable and
gives no offense upon drinking might be polluted with that which
would be detrimental to health. The palatability of water may be due
to the carbonic acid present, which results from the decomposition of
products contained in it.
The carbon dioxide, which is present in rain water, is obtained
from the air through which the rain passes. Carbon dioxide is also
taken up by the water as it percolates through ground covered with
vegetation. The presence of this gas increases the solvent powers of
the water. Water may also contain metal in solution such as iron,
arsenic and copper.
The important foreign ingredients in water are those of organic
origin, such as microscopic plants, vegetable fungi, detritus of
vegetable life, minute insects, infusoria, ova of insects, minute
parasites, and animal debris. Water usually contains millions of
various micro-organisms, mostly harmless, although at times it may
also contain so-called pathogenic germs.
States of Aggregation
Water is formed into the solid state, ice, at zero degrees
centigrade. At 100° C. water boils and is converted into gas or
vapor, although water is contained in the air in the gaseous form
at ordinary temperatures. Between these two limits, 0° C. and 100°
C. water obtains in the liquid form which is its most common state.
Water is the most widely distributed of all the substances. It is
practically incompressible. When heated it contracts until it reaches
4° C, or 39.2° F., and is at this point taken as the basis for
specific gravity of liquids and solids.
Universal Solvent
Water is the most universal solvent known in Nature. Practically
all substances yield to it. Most of the water taken into the body
passes through unchanged, although it is only reasonable to suppose
that some of it is broken up into its elements and united with other
compounds of the body.
Necessity for Water in Body
Water composes about 70% of the entire weight of the body (about
58.5% per volume). A very great amount of water is required by the
tissue for the performance of the bodily functions. As the gears of
machinery must be bathed in oil to prevent undue wear, so must the
tissue cells be bathed in water (secretions) that there be no undue
wear. The tissue cells are spoken of as being aquatic in their habits.
Rosenau in summarizing the use of water in the body says: “It
enters into the chemical composition of the tissues; it forms the
chief ingredient of all the fluids of the body and maintains their
proper degree of dilution, and thus favors metabolism; by moistening
various surfaces of the body, such as mucous and serous membranes, it
prevents friction; it furnishes in the blood and lymph a fluid medium
by which food may be taken to remote parts of the body and the waste
material removed, thus promoting rapid tissue changes; it serves as a
distributor of bodily heat; it regulates the body temperature by the
physical process of absorption and evaporation.”
Chemically Pure Water
Chemically pure water can be obtained only by distillation; it
is undesirable, however, for drinking purposes because of its
insipidity. Before such water is agreeable for drinking it must
be aerated; this may be accomplished by agitation or by passing it
through a porous substance containing air. One of Nature’s methods
of aerating water is found in mountain streams where the water flows
down over rocks. The same thing is accomplished by fountains and
waterfalls. It is the mineral matter and the gases held in solution
that give water its taste, and it is the difference in these minerals
and gases that causes the individual to dislike the taste of water
which he is not accustomed to drinking. But this is purely a matter
of taste and has no value from a hygienic standpoint, for the most
impure water, water that contains so-called pathogenic germs, may
taste very good.
Turbid or muddy water is not necessarily impure from a hygienic
standpoint when found in rivers, but when subsoil water becomes
turbid it should be regarded with suspicion.
Hard and Soft Water
The question of hard and soft water is one that must of necessity
receive some consideration, but it is of more importance from an
economic standpoint than from a sanitary standpoint. Soft water is
generally considered to be more desirable for drinking purposes,
and it is certainly more desirable for cooking. From an economical
standpoint, soft water is more preferable as the hard water requires
more soap to produce a lather.
Hardness of water is spoken of as being temporary or permanent.
If the water remains hard after having been boiled it is known as
permanently hard water. Hardness of water is due to the presence of
the soluble salts of the alkaline earth metals, especially calcium
and magnesium. Temporary hardness is due to calcium or magnesium
carbonate held in solution as a bicarbonate by the dissolved carbon
dioxide. The hardness is temporary because the carbon dioxide is
driven off by boiling, and the soluble bicarbonates are precipitated
as insoluble carbonates.
Permanent hardness, on the other hand, is due mainly to sulphates
and chlorides of calcium or magnesium. These salts are stable and
therefore are not precipitated by boiling.
Elimination of Water from Body
Water is excreted from the body through the various channels. The
kidneys excrete about 50%, the lungs about 20%, the skin about 28%,
while the other 2% is excreted through the feces and other minor
channels.
Amount of Water Needed for All Purposes
The amount of water needed for all purposes varies just the same
as the amount of water needed by the body varies with conditioning
factors. The locality and the climate will enter into the
consideration of the amount of water needed to meet the requirements
of hygiene and sanitation.
The amount of water required by the human body in twenty-four
hours varies with many factors. The age of the individual and his
occupation and health, and climate would be conditioning factors.
However, authorities are pretty well agreed as to the amount
necessary. It is estimated that the body requires a little less than
one gallon of water per day, about two quarts taken as drinking water
and the balance in food.
There is a wide range of difference in the amounts estimated, for
under some conditions, a minimum of seventeen gallons, or even twelve
gallons, would be sufficient, while under other circumstances and in
other localities as much as 300 gallons per day per individual would
not be an excessive or wasteful amount. The average amount estimated
per individual per day for domestic purposes is placed at seventeen
gallons for all purposes. In 1918 the statistics showed that Buffalo
used an average of 260 gallons per capita per day, but many cities
used much less. In Berlin in 1913 the water consumption amounted to
an average of twenty-four gallons per capita per day.
The hygienic importance of these figures is insignificant since they
are only approximate. There are a number of factors that are not
taken into consideration. The figures are estimated on the number of
gallons of water pumped and no account whatsoever is taken of the
water waste through precipitation and loss through leaky pipes. Some
engineers maintain that fully half the water pumped is lost in these
various ways. Another thing that must be considered when comparing
the amount of water used by different cities is the industries. Some
industries require much more water than others, therefore, if a
just comparison is to be made between cities only the water that is
actually passed through the private meters must be considered.
Water Waste
Consideration of the subject of water would not be complete without
some reference to the amount of water that is wasted. It seems a
small matter to waste water. We sometimes say there is plenty in the
river. But the proposition of preparing the water for use and getting
it to the individual for consumption may involve many phases of
hygiene from several different angles and one of these angles may be
industrial hygiene. To get water into the home and factory requires
a great many processes such as laying and maintaining water mains,
purifying the water and pumping. This involves several industries and
trades, so the problem of a water supply is far reaching and is of
vital importance to the community.
There should never be a sacrifice on the part of hygiene and
cleanliness for the purpose of saving water. A sufficient amount
of water should at all times be insisted upon, but certainly there
should be a strenuous effort to eliminate undue waste.
The main causes of water waste will be found to be leakage in mains
and service pipes and waste from defective fixtures in the house.
All of this leakage and waste should be properly attended to because
of the direct relation which it bears to hygiene and particularly to
industrial hygiene.
The introduction of meters has been an important factor in reducing
water waste. It is not the thought to limit the amount of water used
or to deprive one of a sufficient amount, but there is nothing to
be gained by an unnecessary waste. The introduction of meters in
Milwaukee reduced the amount of water used per tap from 1,781 gallons
per day to 644 gallons per day without putting any restrictions upon
the consumers. It is an enormous task to provide a sufficient amount
of pure clean water for a large city and certainly an effort should
be made to avoid waste.
SOURCES OF WATER SUPPLY
Rain Water
The sources of our water supply may be classified as: Rain and snow
water, surface water and ground or subsoil water.
The rain and snow water provide a supply for domestic purposes.
This source cannot be relied upon in some sections of the country
because of the variable amount of rain fall. Rain water is pure from
the fact that it has been vaporized and then condensed the same as
in distillation; but it does not remain long in this pure state
since it is exposed to so many sources of pollution. This water is
collected in receptacles called cisterns and tanks and used mostly
for household purposes. It can readily be seen that water thus stored
might become polluted from the surfaces with which it comes in
contact. To prevent this special care would be necessary, and in the
majority of cases the need for this precaution is not recognized.
This source of water supply is not very desirable since its quantity
is variable and also because of the difficulty in storing large
quantities and in providing protection so that it will not become
contaminated and thereby rendered unfit for household use.
While rain water in its unpolluted state is a pure water, it is
not suitable for drinking purposes until it is properly aerated.
The air contains dust and other suspended impurities which will be
precipitated with the rain and thus pollute the water. However,
the amount of pollution is so small that it is of little sanitary
importance. After the air has been cleared of these suspended
impurities the rain water will be relatively pure. It will be noticed
that after a rain the air seems clear and clean; this is due to the
rain actually washing the air.
It is necessary to filter rain water collected from the surface of
roofs because roofs collect impurities from smoke and dust. The
average filter used for this purpose is usually inadequate and
receives such little care that it is of slight value.
In the large cities or even in the larger towns the cisterns have
been replaced with more modern and more satisfactory means of water
supply. Rain water is soft and therefore is most desirable for
laundry purposes and is also very desirable for cooking. It is not
considered as satisfactory for drinking, however, as ground water or
properly filtered surface water. It always contains gases such as
nitrogen, oxygen, and carbon dioxide. The amount of solids varies.
The storage of water in cisterns forms a good breeding place for a
certain kind of mosquito, stegomyia calopus, which is supposed to
cause yellow fever; but regardless of the supposed pathogenicity of
this mosquito it is quite objectionable.
Surface Water
Surface water is derived from ponds, lakes, rivers and creeks; in
fact, any water which is in contact with the atmosphere is known
as surface water. Surface water forms really the most desirable and
satisfactory source of public water supply.
=Streams= form natural sewers for the regions which they drain and
ponds and lakes form convenient dumping places for the sewage carried
by the streams, therefore it will readily be seen that the surface
water is liable to great pollution from these sources. It therefore
becomes necessary to purify it by some means before it can be used
for domestic purposes.
At one time it was thought that streams purified themselves in their
flow, but this is now disputed and has been proven to be erroneous
and should be strenuously denied. There are many factors at work in
Nature which purify water in its natural state. Before civilization
brought about so many artificial and unnatural conditions it was
true that, with the small amount of waste material emptied into the
streams, Nature would, through her natural processes, keep the waters
of the streams in a state of natural purity. But in the present day
with not only the sewage of our large cities pouring into the rivers
and lake, but also the waste material from factories and different
industries, it becomes necessary to use some artificial methods for
water purification.
=Lakes=, from a sanitary standpoint, form a more desirable source
of public water supply than rivers. There are several reasons
for this. First: there is possible a greater dilution of the
impurities that reach the lake. Second: there is greater opportunity
for sedimentation which is a very important process in water
purification. Third: the water is softer than river water and freer
from organic impurities.
The greatest problem that a city getting its water supply from a lake
has to solve is how to keep its sewage from polluting its own water
supply. To prevent this, it is necessary to place the intake for
the water supply far out in the lake. The danger from pollution has
become so great in some places, as in Chicago, that special canals
have been constructed to carry the sewage into other channels rather
than empty it into the lake.
The impurities from the sewage may travel a great distance into the
lakes. Serious sewage pollution was found ten miles out in the lake
from the mouth of the Detroit River. Pollution has been found as far
as eighteen miles from the shore in some places.
So it is readily observed that, notwithstanding the fact that the
lakes and ponds furnish a more desirable public water supply, yet
this source is not, by any means, free from objections.
The =impounding reservoir=, which is an artificial reservoir for
the purpose of storing up water, is another very reliable source
of public water supply. These reservoirs are often built in the
mountains by placing a dam across a ravine or canyon. The largest
dam in the world is the New Croton across the Esopus Creek in the
Catskill mountains in New York. It is 248 feet high, 185 feet thick
at the bottom and eleven feet thick at the top. This impounding
reservoir furnishes an addition to the water supply of New York City.
There are many advantages to the impounding reservoirs, but there
are also many disadvantages. One advantage is that the area drained
is comparatively small and therefore the pollution from that source
is lessened; also the storage factor which is experienced in this
reservoir is an advantage. In this way many of the so-called
pathogenic microörganisms die before they are carried to the
consumer. A disadvantage is that they are open to the atmosphere
and light and this is conducive to stagnation because the water is
still. This results in an increase in the growth of algæ and other
microscopic organisms. The stagnation of the water results in an
increase of the products of decomposition. This, together with the
microörganisms and algæ, produce the foul smell and bad taste of the
water.
The stagnation of impounding reservoirs and small lakes may become a
vital factor from a hygienic standpoint. If the water is less than
twenty feet deep it will be kept in motion by the wind and in this
way will not become stagnant, but if it is more than twenty feet
deep the lower portion will remain still. This prevents the water
from mixing and therefore the under portion will become stagnant
while the surface will not. If the water supply is taken near the
surface there will not be so much danger from the stagnant water,
but even then there are times of the year when there is a complete
stirring up of the water. This mixing of the surface water and the
bottom water takes place twice a year, in the spring and in the fall.
This mixing is the result of the changing of the temperature of the
surface water. During the summer the surface water becomes warm and
the temperature may reach 80° F. In this way the warm water remains
on top but is kept stirred up by the wind. The wind will not usually
create a disturbance for more than twenty feet except in very large
lakes where it may be as great as forty feet.
As winter approaches the water cools until finally the temperature
of the surface water becomes the same or more nearly the same as the
bottom water. Then the wind exerts a deeper influence and the surface
and deep water will mix. During this process vertical currents may
be produced. This mixing continues until all the water has been
thoroughly mixed and until the temperature of the surface water goes
below the point of maximum density which occurs at 4° C. The cold
water accumulates on the surface where ice is often formed. In the
spring the process is just reversed. The fall mixing of the water is
much more thorough and intense than the spring mixing.
The changes brought by this mixing are obvious. The surface water
contains a large amount of oxygen. The bottom water contains much
less oxygen but a great quantity of decomposed products. The oxygen
is carried to the bottom and there oxidizes and neutralizes some of
the products of decomposition.
The =sources of impurities= in surface water are various. One of the
most menacing sources is from the sewage which is carried from the
centers of population. In the rivers it is the sewage of the towns
and cities situated above. In the lakes it is usually the sewage of
the city itself that is likely to pollute its own water supply. Under
the present conditions it seems that it is easier to purify the water
supply than to purify the sewage or provide some other method for its
disposal.
Naturally the water of rivers is purest near the source. The reason
for this is that the rivers form a natural drainage for the land
through which they flow. The waste products from every process
carried on in that territory find their way into the streams as a
natural result of the law of gravity. The water will be found to
contain large amounts of mineral and organic matter after passing
through populated and cultivated areas. Purification of rivers is
considered under Water Purification.
Ground or Subsoil Water
In the consideration of the three sources of water supply it is
difficult to draw definite lines of demarcation since the rain and
snow water soon becomes surface water and the surface water may
percolate through the ground and become subsoil water.
=Well water and spring water are classed= as ground or subsoil water.
From a hygienic standpoint water obtained from wells or springs forms
a very reliable and satisfactory source of supply.
Especially is well or spring water desirable for private domestic
use, since it is usually in a reasonable degree of purity and does
not, therefore, require any artificial process for purification. The
sources of water supply used for public purposes, made necessary
because of the volume of water required, are not so satisfactory for
a private or domestic supply because its purification would entail
too great an expense to warrant the practicability on such a small
scale. Therefore, the most desirable source when only a limited
amount of water is required is the wells.
Wells may be used for public water supply and are in some of the
smaller towns, but they are not so practicable as their supply is
likely to be inconstant. In other words, there is danger of the wells
going dry, and since they are put down at a great expense, this would
be too great a risk to take even though the water thus obtained is
satisfactory from a hygienic standpoint.
[Illustration:
The above illustration shows the fluctuation of ground water. When
the ground water is at the low mark the shallow well becomes dry;
as the water rises it flows into the well. When the water has
reached the high mark the intermittent spring becomes a flowing
spring. The pressure of the ground water is great enough to produce
flowing wells down on the level.]
Not all wells, by any means, will furnish a pure water supply. There
are many factors to consider from the viewpoint of the pollution
of well water and these will be considered in due time. When water
reaches an impervious strata it remains at that level and moves in a
horizontal plane. Water may form in beds or be found in underground
streams. It is only in the limestone regions that water forms in
streams under the ground.
[Illustration: Poorly constructed well, polluted by seepage thru
limestone.]
The depth at which water is found beneath the surface varies. The
water directly beneath the surface, or that which is derived from
surface drainage and the rainfall, is, by some, styled the ground
water. This is the shallow water. That which is found at a lower
level is called the lower subsoil water or underground water.
The ground water does not provide a very desirable source of well
water because there is danger of pollution from the surface. The
degree of this impurity will depend largely upon the character of the
soil. If it is sandy and thus provides a good filter medium there
is little danger from pollution; but if the soil is of a limestone
formation it makes a very poor filter and the shallow water is likely
to be polluted from the surface drainage.
The subsoil water moves in the direction of the nearest body of
water. That is, if it is near a river or lake its movement will be in
the direction of this river or lake. For this reason a well near the
seashore will contain fresh water.
In wells less than fifty feet deep the temperature of the water will
be influenced by that of the atmosphere. It will be warmer in summer
and cooler in winter. Some authors put this depth at much less than
fifty feet, maintaining that the atmospheric temperature will have no
influence whatsoever at such a depth. It is true, however, and the
fact is undisputed, that in wells 50 feet deep or more the water is
cool and the temperature remains constant. It is not influenced by
the change in atmospheric temperature.
Sand and gravel deposits form the best source through which to obtain
subsoil water. To supply any very great amount there must be a number
of wells and these must be far enough apart so as not to draw from
the same territory. Seventy-eight million gallons of subsoil water
per day is provided at Brooklyn from twenty-four separate pumping
stations. Memphis, Tennessee, is the largest city in the United
States which gets its entire water supply from sand and gravel
deposits.
[Illustration: Poorly constructed well, polluted by surface drainage.]
Sandstone rock furnishes an excellent source for subsoil water since
it makes an excellent filter. Because of the limited amount of water
obtained in a sandstone formation this source is practicable only for
a very limited supply.
Limestone formation is the most undesirable source of subsoil water
supply from a hygienic standpoint. Limestone is not porous and
therefore has no filtering qualities. If water does pass through this
sort of a formation it must travel through its crevices and fissures.
It is very difficult to know where the pollution of water passing
through limestone originates. As these fissures are usually very
long, and as the water is in no way filtered as it passes through
them, the contamination might enter the water at a point far distant
from where the well is sunk. The water supply from limestone is
likely to be inconstant because the water is not contained in the
limestone, but flows through the cracks and crevices. In this way it
may soon flow away unless the source is replenished by rain or snow.
Water from the subsoil is obtained, as has been stated, from wells.
Wells are classified as shallow and deep. By a shallow well is
commonly meant one that is dug and not more than thirty feet deep.
This type is usually walled up with brick or stone and is from five
to six feet in diameter. Shallow wells may also be driven. That is,
a gaspipe with a sand point is driven into the ground until the
water-table is reached, the water being pumped out with an ordinary
suction pump.
Shallow wells must never be considered a satisfactory source of water
supply where there are conditions existing which would result in such
pollution of the ground that the water percolating through can not be
more or less filtered. Sewage polluted soil never is satisfactory for
shallow wells.
[Illustration: Showing a properly constructed well in unsanitary
locations.]
Deep wells are drilled and are from six to eight inches in
diameter. The water from deep wells may be free from contamination
but may contain a great deal of mineral in solution and different
salts which render it permanently or temporarily hard. This decreases
its value from a sanitary viewpoint and more particularly from an
economic standpoint.
Special attention should be given the construction of the well. The
casing or walls should be as tight as possible. Special care should
be exercised against the possibility of surface water percolating
through the casing as this drainage will bring impurities.
The casing should project far enough above the surface of the ground
to insure against water running from the surface. It should extend at
least eighteen inches above the ground. The well should have a tight
covering.
The ground possesses great filtering qualities and therefore great
quantities of impurities will be taken from the water as it filters
through. The danger is when the ground becomes so filled with
impurities that its filtering qualities have been destroyed or when
there is not sufficient distance between the source of pollution and
the water level; also when the soil is of a limestone formation and
the water, instead of percolating through it, passes through cracks
and crevices, in which event it will in no sense be filtered.
It was at one time considered that wells should be ventilated and
a great deal of stress was laid upon it. When it is taken into
consideration that the water under ground is in no way ventilated
except through the natural means, it will readily be understood that
it is not necessary to provide ventilation merely because the water
has been tapped by a well.
If the origin of pollution, such as cesspools, is too near the
well or the well is too shallow, not allowing enough distance for
purification, there will be great danger from such sources. The
greatest danger is in the shallow wells. However, these are entirely
satisfactory as a source of domestic supply, providing the soil is of
a sandy or gravel formation and there are no barnyard or cesspools,
for example, too near the wells. A shallow well in a limestone region
is not satisfactory and should be discarded when at all possible.
If it is necessary to use such, every precaution possible should be
taken to eliminate the possibility of contamination.
METHODS OF PURIFICATION
Natural Methods of Water Purification
In considering the subject of water purification it is not our
thought to go into detail and explain the processes that are
necessary to accomplish a pure water supply, but to deal with the
subject in a general way that we may appreciate what is necessary in
this line.
We will first take note of the methods used by Nature in purifying
water. Nature’s method of obtaining chemically pure water is by
evaporation and condensation. The result of this method is the snow
and rain water. About three-fourths of the earth’s surface is covered
with water. The sun acts as a great furnace and the atmosphere as
a vast still. In this way we see that a great quantity of water is
distilled and returned to the earth in a state of purity. It is
estimated by Summerville that “186,240 cubic miles of water are
annually raised from the surface of the globe in the form of vapor
chiefly in the intertropical seas.”
It is entirely erroneous to assume that the impurities in water
are eliminated by freezing. Ice may contain great quantities of
impurities, even so-called pathogenic germs. It has been shown that
many germs are not destroyed by freezing. It is true, however, that
ice will be purer than the water from which it is taken.
There are certain processes which result in a purifying influence as
water is crystallized. As ice forms it excludes suspended matter and
even under certain conditions will exclude dissolved substances. It
will thus be seen that even though ice may not be pure, the danger
from its use is greatly reduced. It is not advisable to use water
from melted ice for drinking purposes.
Manufactured ice is supposed to be free from impurities, but this is
not necessarily true. If ice is produced artificially from distilled
or properly filtered water it will naturally be pure, provided it
does not become polluted in the process of manufacture.
At one time it was believed that river water would become pure in
a flow of seven miles. This, however, could not be true since the
distance of the flow is of less importance than the time required for
the flow.
The greatest aid in this method of water purification comes from
the impurities mixing with the volume of water as it flows. The
impurities become diluted and if sufficient time elapses the bacteria
and microörganisms will die a natural death.
The principal process involved in self-purification of water is
the oxidation of nitrogenous organic matter which is a chemical
process. In the course of time the microörganisms die as a result
of the biological action. Then there is the effect of dilution,
sedimentation, especially in lakes and still water, and the effect of
sunlight.
Food for the bacteria is lessened as a result of the destruction of
the organic matter through oxidation. The minute infusoria, amœbæ
and water worms feed upon organic matter and bacteria and thus aid
in the process of purification. The plants known as algæ play a very
important part also in water purification. They take up the organic
substances and perform other functions similar to the vegetation on
the land. The purifying effects of water vegetation is very important.
One of the chief sanitary safeguards in Nature is dilution. A small
amount of pollution may be quickly diluted by a volume of water until
it is practically harmless. In its concentrated state, however, there
might be enough poison, the strength of which would be greater than
the internal resistance of the individual. This would produce toxic
conditions, or it might even be great enough to produce subluxations.
=Sedimentation= is another of Nature’s methods that is of great
value. This process has been aped by man in the coagulation produced
by the use of chemicals. This action is largely mechanical. During
the process of sedimentation it is only the suspended matter that
settles; but it is maintained that the bacteria and microörganisms
become entangled and are carried to the bottom and in this way the
water is freed from more than simply the mechanical impurities. If
allowed to remain in storage a sufficient time, the harmful bacteria
will die a natural death. There are processes, however, that take
place during the time of storage which are objectionable, but these
relate more to the taste or smell of the water than to the production
of harmful ingredients.
During sedimentation there is a natural settling of the suspended
particles. Not only is the desired result obtained in freezing the
water of solids, but as the suspended matter sinks to the bottom many
of the bacteria will also be carried down. Sedimentation, however, is
not a method that can be used promiscuously. It is usually employed
in connection with some other method; with a slow sand filter, for
example, or when mechanical filtration is used.
Sunlight is Nature’s greatest germicide. Direct sunlight destroys
germ life and renders much aid in maintaining sanitary environmental
conditions. It has a purifying effect upon water in this way. When
the water is in motion or during times of turbidity great good is
accomplished from a sanitary standpoint by the direct rays of the sun.
Artificial Methods of Water Purification
The only way to obtain chemically pure water is by distillation.
However, since this method is very slow and expensive, it is not at
all practicable for the purification of even a private water supply,
and since a chemically pure water is not required for drinking or
other domestic purposes it would be entirely unnecessary to provide
it. Again, distilled water is not desirable for drinking purposes
since its taste is insipid until it is aerated.
When only a small amount of water is required it may be freed of
organic poisonous substances by boiling. This will not, however,
render water that contains lead and other stable chemical substances
injurious to health safe for domestic use.
[Illustration: Sand Filter.]
The dissolved gases are given off by boiling and this leaves the
water with a flat taste which may be improved by aerating; this may
be done by stirring or by placing the water in a jar and shaking it.
=Filtration= is by far the most practicable method of water
purification. There are many different methods used. The two most
used are known as the natural and mechanical.
Under what is known as the natural methods, the sand filter seems
to have precedent. The efficiency of this filter depends upon the
material used, the velocity of the water through the filter and the
care, such as proper cleaning which the filter receives.
As a matter of information the student should become somewhat
familiar with the general construction of a sand filter. The size
of the filter, that is, the area it covers, will be governed by the
amount of water to be filtered per day, which in turn will depend
upon the demands. The greatest objection to a slow sand filter is
that a very large tract of land is required to provide sufficient
surface for the percolation of the water.
The bottom and sides of the filter-beds are water-tight and are
constructed of cement with proper drains to carry off the filtered
water. A layer of very coarse gravel is placed on the bottom of the
filter, then on top of this is a layer of fine gravel. This is then
covered with fine sharp sand about three feet deep. Ordinarily the
entire filter medium is from four to six feet deep.
On top of this layer of fine sand a thin scum is formed which
increases the efficiency of the filter, its action being biological.
As this scum accumulates it becomes necessary to remove it. This
is done by special devices. It is necessary to remove only a small
portion of the sand, for it will be clean immediately below the
surface. This process is continued until the layer of sand has
decreased in depth to about twelve inches when it is replenished with
new, or with polluted sand which has been removed and thoroughly
washed with filtered water.
The filter is first filled by admitting water from beneath for the
purpose of forcing the air out. The depth of water is kept about
three feet above the sand.
The rate of filtration is controlled and kept at a velocity of about
two inches per hour. At this rate a filter of one acre area will
provide about 3,000,000 gallons per day.
A first class slow sand filter should free the water of 99% of the
bacteria. Hygienists claim that filtered water should not contain
more than 100 bacteria to a cubic centimeter. Water from a new filter
or one that has just been cleaned should be tested before it is used.
By this method one can determine whether the desired results are
being obtained.
It may be necessary to store the water in reservoirs before it is
passed through the sand filter for the purpose of sedimentation.
This will rid the water of the small particles of sediment which is
contained in the turbid water. If turbid water is passed through a
sand filter the smallest particles will pass on through with it. This
causes a tendency to fill the filter with clay and other substances.
Instead of the water passing slowly through the sand, it is forced
through in mechanical filtration. The sand is contained in cylinders
or tanks and the water is forced through either as the result of
gravity and weight of the water above or by mechanical means.
Before it is passed through the sand in the mechanical filter, it
is treated chemically to coagulate and precipitate the suspended
impurities. This process is not only mechanical in the sense that
it is accomplished by means of certain machinery, but the action on
the water is mechanical. There is no bacteriological action which
is so essential as this mechanical action in the process of water
purification.
The mechanical method of water filtration has not been found to
be as satisfactory as the slow sand filter process, although very
large amounts of water may be filtered in much less time. One great
disadvantage of this method is that the filters require such frequent
cleaning and in this respect are very expensive to maintain.
=Chemical purification= is not considered by some hygienists as a
satisfactory method for purifying large water supplies. There are
many objections to this method. Even though the water is freed from
the impurities it has received in its natural course, it is laden
with chemicals that may be as injurious to health as the impurities
themselves.
The chemicals used are: Chlorine, bromine, copper sulphate, metallic
iron, ozone and sodium bisulphate.
Swimming Pools
In connection with the subject of water a word relative to the
sanitation of swimming pools will not be out of place. There are many
municipal swimming pools in operation and while they are intended to
improve the sanitary conditions, they may at the same time become a
great menace to hygiene if they are not properly conducted.
No individual should be allowed to enter a swimming pool without
first having taken a shower bath with a liberal use of soap. No one
should be allowed in the pool who is infected with skin dis-eases
of any kind, ulcers, running sores, conjunctivitis, or venereal
dis-eases.
The water should be properly filtered when it enters the pool and
there should be a constant process of disinfection. There should be
not only right construction, but also fit maintenance of the pool.
The swimmer should be properly instructed relative to swimming pool
sanitation.
SEWAGE AND REFUSE DISPOSAL
Methods of Sewage Disposal
One of the greatest problems the hygienists and sanitary engineers
have to solve is the disposal of sewage and refuse without
contaminating the water supply and in other ways rendering the
environment unhealthful.
The methods used for the immediate removal of sewage may be either
the dry method or the water method. By far the more common one in
towns and cities is the water carriage system. In small towns,
however, the more prevalent way is to provide a house some distance
from the dwelling which contains a privy vault.
Where sewage is removed by the water method and carried through
sewers to the waterways, such as rivers and lakes, the great problem
which the sanitary engineers have to solve is how to dispose of the
sewage and not pollute the water supply of the city.
When there is a sufficient amount of water to insure proper dilution
sewage may be emptied directly into it without treatment. But where
there is a limited amount of water, as in a small stream, and a
very large amount of sewage to be disposed of, the water may become
overloaded and thus the supply of other towns become polluted.
When sewage is disposed of in the ocean, oyster beds may become
contaminated as well as the bathing beaches.
Sewage Purification
It is considered cheaper and at the same time satisfactory from a
hygienic standpoint to depend more upon proper filtration than upon
any other method of purification.
There are many different methods used for sewage purification. Sewage
may be screened. This frees it from the larger particles. It is then
placed in tanks and by a slow process of sedimentation relieved of a
large amount of the suspended matter that passes through the screens.
After these processes it may then be carried to fields for subsurface
irrigation. It is carried through porous tile pipes ten to eighteen
inches below the surface and two feet to three feet apart. In this
way the sewage seeps through into a sandy soil. An acre will take
care of the sewage from 150 to 250 people a day. This method can not
be used at all in clay soil.
The crude sewage may be applied to the surface of the land and
carried by means of ditches, but this is not considered satisfactory.
Sand filters are also used, but they require frequent cleaning and
renewing.
According to Price the most desirable method of sewage disposal is
known as the septic method. In this method the sewage is sorted and
the action that follows is bacteriological. The bacteria present act
in the absence of air or oxygen. The sewage thus undergoes a process
of decomposition, fermentation and purification.
The next step is to pass the sewage that has come from the septic
tank through open sand filters very slowly. These sand filters must
be properly cleaned and renewed at regular intervals and must at no
time be overloaded. This makes the effluent from the filter beds
entirely free from germs and harmful matter. It is not necessary for
us to consider the construction of these septic tanks. There are any
number of different types, but the results are supposed to be the
same. The construction of such tanks is in the province of sanitary
engineering and not in that of practical hygiene.
Price states that the water which comes from the filter beds after
the sewage has first been through the septic tank is free from
injurious substances, is capable of supporting life and that even the
drinking of it has been known not to be followed by injurious results.
Refuse Disposal
Another great problem is the disposal of refuse such as ashes,
garbage, and in the larger cities, street sweepings. It is estimated
by Whipple that in the larger cities like New York the refuse will
be in round numbers a ton per capita per year. This is an enormous
amount of material and the disposal of it becomes a great problem.
This is not only of hygienic importance, but also one of economical
significance.
The collection of waste material is objectionable from the social
viewpoint; also an accumulation of ashes and dust will irritate
the eyes and respiratory tract, while piles of garbage and other
filth are conducive to the breeding of flies and mosquitoes. Such
collections result also in the development of ill-smelling odors and
unsightly streets and alleys.
There are different methods used to dispose of this waste material.
It may be collected and burned. This method is called incineration.
Or the refuse may be collected separately and disposed of. When it
is to be disposed of separately there are usually city ordinances
which require the householder to keep the garbage and ashes separate
and they are then collected by the city in separate wagons. In most
cities tall garbage cans are required and the garbage is drained and
wrapped in paper, the ashes are placed in cans or containers. They
are used for filling in low lands while the garbage is taken away and
buried or burned.
For the collection of garbage specially constructed wagons or carts
are used. The garbage must be collected frequently and at regular
intervals before it becomes decomposed and gives off objectionable
odors. The wagons must be properly cleaned for the same reason. In
the removal of ashes and other refuse, care should be taken not to
create a dust and the wagons should not leak so as to litter the
streets and alleys.