_QUALITY OF WATER_
A pure water-supply has always been regarded as desirable and its value
can hardly be overrated, from the standpoint of health, happiness, or
economy. From the earliest history, no crime has been so despicable as
that of deliberately poisoning a well from which the public supply was
obtained, and in the past no charge more quickly could stir the populace
to riot. In Strassburg in 1348 two thousand Jews were burned for this
crime charged against them; and as late as 1832 the Parisian mob,
frantic on account of the many deaths, insisted that the water-carriers
who distributed water from the Seine, shockingly polluted with sewage as
it was, had poisoned the water, and many of the carriers were murdered
on this charge.
Yet no water, as used for drinking purposes, is absolutely pure,
according to the standards of chemistry. Distilled water is the nearest
approach to pure water obtainable, and it is said by physicians that
such water is not desirable as a habitual and constant beverage. The
human body requires certain mineral salts particularly for the bones and
muscles, and while these salts are provided in a large measure by food,
a number are also furnished by drinking water. On the other hand, a
wonderful natural process is accomplished by distilled or approximately
pure water in that the water tends to dissolve, to add to itself, and to
carry away whatever excess of solids may exist in the body. For certain
kidney diseases, for example, pure water is prescribed, not merely as a
means of preventing further accretions, but for the purpose of
dissolving and removing the undesirable accumulations already existing.
Practically, considerable latitude is possible in the matter of the
purity of drinking water, and no particular harm is to be apprehended by
the constant use of either a water containing as little as ten parts per
million of total solids or of water containing as much as three hundred
parts per million of total solids. The human body, in this as in so many
other ways, is so constituted as to be able to adjust itself to varying
conditions of food, and, until an excessive amount of ingredients are
absorbed, no great harm is done. There are, however, certain definite
substances--animal, vegetable, and mineral--which, when found in water,
are decidedly objectionable, and it is not the amount of foreign matter
in a water-supply, but its character, which is of importance in a water
to be used for drinking.
_Mineral matter in water._
The mineral matter is the least objectionable as it is also the most
common, since all water is forced to partake, more or less, of the
nature of the rocks and soil over which it passes. Good waters contain
from twenty to one hundred grains per gallon of mineral salts; that is,
of various chemical substances which are able to be dissolved by water.
If the amount is much in excess of one hundred parts, the water is
noticeably "hard," and this may increase to a point where the water
cannot be used. For example, the writer once superintended the locating
and drilling of a well which passed through a bed of sodium sulphate or
gypsum, just before reaching the water, so that as the latter rose in
the well it dissolved and carried with itself a large amount of this
salt, so much that the water was useless. Water containing more than one
hundred grains per gallon of such salts as magnesium sulphate or sodium
phosphate is a mineral water rather than a good drinking water, and
while an occasional glass may do no harm or may even have desirable
medicinal effects, such a water is not fit for constant drinking.
It is worth noting that many attempts have been made to show the
relative effect of various hard waters on the health. A French
commissioner reported that apparently people in hard-water districts had
a better physique than in soft-water districts. A Vienna commissioner
also reported in favor of a moderately hard water for the same reason.
It is to-day believed by many that children ought to have lime in water;
that is, ought to drink hard water to prevent or ward off "rickets" or
softening of the bones. An English commissioner, on the other hand, has
concluded that, other things being equal, the rate of mortality is
practically uninfluenced by the softness or hardness of the
water-supply. This same commissioner has also shown that in the British
Isles the tallest and most stalwart men were found in Cumberland and in
the Scotch Highlands, where the water used is almost invariably very
soft (Thresh's "Water-supplies").
It has been asserted that certain diseases, not necessarily causing
death, are caused by hard water, as calculus, cancer, goiter, and
cretinism; but, as already pointed out in Chapter II, no satisfactory
proof has ever been established. One must conclude that within
reasonable limits there is little to choose between a hard and soft
water for drinking purposes, although a change from a soft water to a
hard, or _vice versa_, usually produces temporary derangements.
_Loss of soap._
For washing purposes the value of a soft water is more marked. When a
hard water is used, a certain amount of soap is required to neutralize
the hardness before the soap is effective, and this takes place at the
rate of about 2 ounces of soap to 100 gallons of water for each part of
calcium carbonate per gallon, or about 3 ounces of soap to 10,000
gallons for each part per million increase in hardness.
The village of Canisteo, New York, has a hard spring water, the hardness
being recorded by the State Department of Health as 162.8 parts calcium
carbonate in a million parts of water. Clifton Springs water has a
hardness of 208. Catskill, New York, which gets its water from a stream
running down from the hillside, has a hardness of 22.1 or 140.7 parts
less than Canisteo. Mr. G. C. Whipple says ("Value of Pure Water") he
has found that 1 pound of soap is needed to soften 167 gallons of water
when that water has a hardness of 20 parts per million, and that each
additional part requires 200 pounds of soap to soften a million gallons.
If Clifton Springs and Catskill should each use 100,000 gallons per day,
the additional cost of the hard water, at five cents a pound for soap,
would be 20 x 140.7 x 0.05 = $140.70, provided all the village water
were neutralized with soap. Probably not over one fiftieth part of the
water is so neutralized, so that the added cost of soap is actually
about $2.80 a day. Whipple expresses this cost as _H_/100 = _D_, where H
is the hardness in parts per million and _D_ is the cost in cents for
every 1000 gallons used for all purposes. Thus Canisteo water costs
162.8/100 = 1.6 cents per 1000 gallons used, while Catskill costs only
22.1/100 or 0.2 cent on account of soap.
This discussion is intended to suggest a comparison between a well of
hard water and a surface supply of soft water, when both are available.
It should arouse an interest in securing a soft water as well as a clear
water, and the advantages of the softer water, in so far as soap
consumption alone is concerned, are seen to be not inconsiderable.
_Vegetable pollution._
The vegetable and animal matter is organic in its origin and nature, and
their effect on water may be taken up together.
Vegetable pollution is generally the result of decayed leaves, roots,
bark, and such other vegetable tissue as would be likely to be found
where the water-supply flows through a swamp or accumulates in hollows
and depressions. This sort of water is likely to have a brownish or
yellowish brown color, to have a slightly sweetish taste, and to be
soft, that is, free from mineral solids. Usually such water can be used
for drinking purposes without serious consequences. AEsthetically, it is
objectionable because of its color, and the city of Boston has expended
many thousands dollars in building channels around swamps and in
providing artificial outlets for swamps, so that the color of the water
collected on the watershed shall not show the color induced thereby.
Water from the Dismal Swamp of Virginia is so discolored as to look like
coffee, and yet, in the vicinity, it is much prized for drinking, and
formerly great pains were taken to fill casks with this water when in
preparation for a long sea voyage.
Such matter always has a marked influence on a chemical analysis of the
water, shows large amounts of nitrogenous matter, and apparently
indicates a polluted supply; but, if the reason for this apparent
pollution lies in the presence of a swamp, no danger to health therefrom
is to be apprehended. Such water also is less subject to decay or
putrefaction, and if a water-supply for a house is to be taken from a
small pond, a gathering ground containing swamps is likely to furnish a
more satisfactory water, color alone excepted, than one free from such
swamps.
_Pollution of water by animals._
Animal pollution usually comes from the presence on the watershed of
domestic animals, that is, cows, sheep, and horses, or from manure
spread on fields draining into the brook, or from barns or barnyards
close by the water. It is the presence of this sort of pollution that
furnishes the other kind of organic matter not to be distinguished by
chemical analysis from the organic matter just referred to, but vastly
more objectionable.
Drainage from houses and barns is responsible for the same kind of
animal pollution, and while it is difficult to prove by statistics that
such pollution is always dangerous to health, it is sufficiently
repulsive from an aesthetic standpoint to be done away with whenever
possible. Such pollution applies only to surface water, such as brooks
or lakes, and the best method of detecting and evaluating this pollution
is to make a careful inspection of the watershed.
If it is proposed to use the water from a certain stream for drinking
purposes, the first step should be to examine carefully the area
draining into the stream, to detect, if possible, all opportunities for
animal wastes to find their way directly into the stream and to note
whether fields sloping rapidly to the streams are manured; to see
whether the stream flows through pasture land in which cows are kept,
and especially to note whether houses with their accompanying
outbuildings are near enough the brook so that water may at any time
wash impurities down into the stream. Whenever a brook flows through
woodland free from all animal pollution and not subject to pollution
before entering the wood, the water is probably as pure as that in any
spring or well.
On the contrary, when the water in a brook flows through a meadow used
for pasture or through gullies, the sides of which are manured, or in
the vicinity of houses and barns, the water is probably unfit for
drinking purposes. This can be realized by standing at the edge of a
barnyard and watching the rain falling first on the roof of the barn,
then in larger quantities from the eaves on to the manure pile into the
yard below, then accumulating in pools of reddish black concentrated
liquid, until the volume is sufficient to form small rills which
gradually assemble into a fair-sized stream. Similarly, the pig-pen
drainage is washed out from under or even through the building, and,
after combining with the barnyard drain, is carried into the stream near
by. The very idea of drinking such filth is nauseating in the extreme.
It is common for small slaughter-houses to be built on the side of a
stream, so that the offal, carrion, and refuse of the place may be
carried off without effort on the part of the owner, and there are a
number of such places where brooks, used as places of deposit for
slaughter-house refuse, discharge directly into the reservoirs of water
works.
But this sort of animal refuse is not the most serious pollution. The
leachings and washings from privies and cesspools, carrying, as they do,
germs of contagious diseases, are most to be dreaded, and when a privy
(with no vault underneath) is built on the side of a steep ravine and is
so located that the natural drainage of the sidehill on which it is
built cannot help but run around and through the building, then the
pollution of the stream in the gulley is not only direct and inevitable,
but of a deadly sort (see Fig. 36). Fortunately, the germs thus carried
into the stream suffer the vicissitudes of all life exposed to the
attacks of hostile forces.
At the time of freshets the streams carry mud in abundance, which mud is
continually settling out of the water as opportunity offers, and with
this settlement of mud there occurs also the settlement of the germs.
Also the pathogenic or disease-producing germs are usually weaker and
more susceptible than the putrefactive and other organisms which are
found in the water in great abundance after any rain storm, and which
tend to inhibit or destroy the pathogenic germs. But some will survive,
and, with favoring conditions, may pass through the water-pipe to the
house, causing sickness, if not death.
[Illustration: FIG. 36.--Stream draining a privy.]
Any inspection of the watershed, therefore, should look to the
elimination of the dangers above described, and to the location of barns
and barnyards, pig-pens and poultry yards, privies and cesspools, so
that no direct drainage into the stream shall be possible.
It is out of the question for any surface water-supply to be pure, since
the mere fact of the passage of water over the soil inevitably results
in the collection of organic matter; and it is no exaggeration to say
that the time will inevitably come in this country, as it has already in
Germany, when no surface supply will be considered satisfactory unless
the water is filtered. The only alternative is water gathered from areas
that are owned by the individual and on which, therefore, all dwellings
may be prohibited, all cultivated land avoided, and where the primeval
forest may be restored, making the watershed equal to that from which
forest streams emerge.
But usually, in the case of a single house, it will not be possible
entirely to eliminate the dangers of surface pollution, although an
inspection will show the dangers, and possibly some of them may be
avoided. Certainly any direct drainage into the streams should be cut
out, as well as the drainage from barnyards in the immediate vicinity of
the point where the water is taken out. Just what percentage of
pollution may be eliminated in this way it is impossible to determine,
but it is not too much to say that no brook or pond should be used for a
water-supply of a house unless _every known pollution_ of an organic
nature has been removed. Under the most favorable circumstances there
will be enough accidental contamination to make the water at times
dangerous, and no added risks ought to be assumed.
In looking over a watershed the possibility of sewage entering the
stream is, of all pollutions, the most to be avoided. To adequately
investigate the quality of a stream, the inspector must satisfy himself
as to the point of discharge of the sewer of every house on the
watershed, and this must be done personally, without apparently
reflecting on the statements of the owner of the house. If any such
points of discharge are found, the sewage should be either diverted into
some other watershed, or spread out over the ground away from the
stream, or purified by some artificial treatment before discharge, or
else the creek water cannot be used.
The next point to be noted in the source of the water-supply is the
presence and location of privies. These nuisances should be as far back
from the banks of the streams as possible to eliminate all danger since
the surface of the ground always slopes toward some stream, and
pollution may be carried for considerable distances over or through the
soil. Water-tight boxes can be provided so that no possible pollution of
the surface-wash can occur, and if periodically the contents of these
boxes be hauled away and buried, the privy loses its dangerous
character. The city of Syracuse has installed on the watershed of
Skaneateles Lake a most admirable system of collection of privy wastes,
and the lake water is thoroughly protected, although there are several
hundred privies on the watershed.
Cesspools, in general, are not dangerous if they are located fifty feet
or more from the stream and if no overflow occurs.
Barnyards ought not to drain directly into streams, but when, as in so
many cases, the stream flows through the barnyard, the only remedy is to
move either the stream or the barnyard, and it is difficult to persuade
even a well-disposed neighbor to do either. It is sometimes possible to
appeal to his sense of right; but, too often, the neighbor feels that it
is his land, his barn, his drain, even his brook, and he will do
whatever he pleases with them, whether the water further down stream is
to be used for drinking purposes or not. The question resolves itself
into an inspection of the watershed and a determination of the existing
conditions. If those are tolerable, the water may be used. If evident
contamination is present, the water must usually be given up, and some
other source of supply sought.
_Well water._
The pollution of wells, if it exists at all, is usually very pronounced,
and it is probably safe to say that, except where buildings, drains, or
cesspools have been crowded too close to wells, or where some manifest
and gross cause of pollution exists, a well water is safe to drink.
To protect properly a well from gross pollution, two precautions should
be observed. The wall of the well should be built up in water-tight
masonry, so that surface wash cannot enter the well except at a depth of
at least six feet, and second, this water-tight masonry should be
carried above the surface of the ground at least six inches and the well
then covered with a water-tight floor so that no foreign matter can drop
through the floor into the well or can be washed in by the waste water
from the pump (see Figs. 28, 29, 30). If these precautions are taken, it
is safe to say that nine tenths of the pollution occurring in isolated
wells would be stopped.
Besides the above, a well may be polluted by a stream of underground
water washing the contaminating matter through the soil. Experiments
have been made to show this very plainly. A large number of bacteria
were placed six feet below the surface just in the top of the
underground stream of water. Within a week they were found in
considerable numbers in the water of the soil one hundred feet distant,
but when the same number of bacteria were placed in the soil four feet
below the surface above the level of the ground water, none of them
found their way into the water of the soil. This experiment shows the
folly of building a cesspool in the vicinity of a well when they both go
down to the same water level, since the contents of the cesspool will be
carried into the well if the underground stream flows in the proper
direction. A shallow cesspool, however, would not be open to the same
objection.
It is always difficult to detect the direction or flow of underground
water, and various technical and delicate methods have been selected to
make this determination. A very simple test, however, is to dig a hole
at the point where pollution is suspected, carrying the hole down to
where ground water is reached, and then to throw a gallon of kerosene
oil into the hole, and if the ground-water flow is toward the well, the
presence of kerosene in the well water will make the fact known. This
would not, however, prove that the actual contamination would produce
disease, since a liquid like kerosene can find its way through the pores
of the soil to much greater distances than bacteria can be carried. But,
to be on the safe side, water from such a well should not be used.
To make sure of the quality of the water proposed for a water-supply, it
is wise to have such water examined by a chemist. The chemist will make
certain determinations of ammonia and other chemical combinations, and
will report his findings with an interpretation or explanation of the
result. What he finds is not the presence or absence of disease or
disease germs, but substances that suggest or involve the presence of
organic pollution. A test is made for the number of bacteria, and a well
of spring water which contains more than about fifty in a cubic
centimeter is a suspicious water. Surface water, on the other hand, may
contain two or three hundred without being necessarily bad, the types of
bacteria being harmless. Generally, a chemist will also determine the
presence of the colon bacillus which is found in the intestinal tract of
man or warm-blooded animals. Wherever this is found, in even such a
small quantity as one cubic centimeter of water or less, there is strong
presumption that the water has been polluted by human wastes and is
therefore not fit to drink.
_Dangers of polluted water._
Since no evidence of the danger of drinking polluted water can be so
graphically expressed as by a direct reference to epidemics caused by
the unwise use of such water, it will not be out of place to refer
briefly to some of the instances in which a direct connection has been
traced between a specific pollution of a certain water and disease or
death resulting from it.
Although, as has already been explained, an infected water causes
various kinds of intestinal disorders, particularly among children, the
most characteristic evidence of pollution occurs when the noxious
material comes directly from a typhoid fever patient, so that this same
disease can be recognized as transmitted to another individual or
family. This transmission of typhoid fever, while in some cases very
plainly due to other agencies than water, as, for example, milk,
oysters, and flies, yet, by far the largest proportion of the
transmitted cases comes through the agency of polluted drinking water,
and there are many examples both of contaminated wells and streams which
emphasize this possibility beyond all question.
Two historic investigations of epidemics which have thoroughly convinced
sanitarians that typhoid fever is a communicable disease and that water
is the vehicle for its transmission may be briefly cited.
In 1879 Dr. Thorne reported an epidemic in the town of Caterham,
England, which he had investigated, and disclosed the following facts:
The population of the village was 5800. The first case of fever appeared
on January 19. Others followed in rapid succession, until the number
reached 352, of whom in due time 21 died.
The possibility of infection was carefully looked into. The influence of
sewer air was ruled out because there were no sewers. The milk supply
was proved unobjectionable. No theory of personal or secondary infection
could account for the widespread prevalence, particularly as only one
isolated case had occurred during the preceding year, and this had been
imported.
Of the first 47 persons attacked, 45 lived in houses supplied with the
public water-supply, and the other two were during the day in houses
supplied with public water. Further, in the Caterham Asylum, with nearly
2000 patients, not a single case appeared, their water coming from
driven wells. Investigation of the water-supply showed the undoubted
cause of the epidemic. The public water-supply was derived from three
deep wells, connected by tunnels in the chalk. In one of these tunnels,
from January 5 to the end of the month, a laborer worked, who, though
unattended by a physician, was evidently suffering from mild typhoid
fever, the symptoms of the disease being carefully detailed by Dr.
Thorne. The laborer at the time of his going to work had a severe
diarrhoea, and while in the tunnel was obliged to make use of the
bucket, in which the excavated chalk was hauled to the top. He admitted
that at times the bucket, in being hauled up, would oscillate in such a
way as to spill part of its contents and thereby pollute the water of
the well below. Two weeks from this accidental pollution the epidemic
began, and there can be little doubt of the relation of this mild case
of typhoid to the epidemic which followed.
A second illustration may be cited at Butler, Pennsylvania, which
occurred in 1903. The water-supply of Butler, a borough of 16,000
people, comes from a reservoir on the creek which flows through the
phase. On account of the gross pollution of the water at the
pumping-station, a long supply pipe has been laid from the reservoir
directly to the pumps. The water also was filtered through a filter of
the mechanical type. Through some accident the filter was thrown out of
service for eleven days, between October 20 and 31, 1903, and
unfortunately, on account of the failure of the reservoir dam, the water
was at that time being taken directly from the creek at the pump well,
and had been since August 27. Only ten days after the filter was shut
down, the epidemic broke out in all parts of the town. Between November
10 and December 19 there were 1270 cases and 56 deaths. In the
subsequent investigation it developed that not only was the stream
generally polluted by the sewage at various points above the intake, but
that there had been several cases of typhoid fever on the watershed,
some on a brook that enters the creek within one hundred feet of the
filter plant. As at Caterham, the inference is patent that the
introduction of some specific infection into the drinking water was the
direct cause of the general epidemic.
The occasional outbreaks of typhoid fever which occur in single families
are not so easy to explain, particularly since the small number of
persons affected does not usually call for a widespread interest on the
part of those experienced in such epidemics. In the Twenty-seventh
Annual Report of the New York State Department of Health, the following
description of an outbreak in a small hamlet, where the cause seems to
have been the use of a pond for a wash tub by some Italian laborers,
thereby transmitting the disease germs from their clothes to the water
afterwards used in a creamery, is given. The diagram, Fig. 37, shows
that the creamery secured its water for the purpose of washing cans from
a small pond by means of a gravity pipe line. The foreman of the
creamery, who boarded at the residence marked _A_, first contracted
typhoid fever. A week later an employee at the creamery also contracted
the fever, the residence of the latter being marked _B_ on the diagram.
About six weeks later the railroad station agent, living at the point
marked _C_, contracted the fever, and two weeks later his wife was
attacked with the same disease. The residences at _B_ and _C_ are only
about three hundred feet apart, both families taking their
water-supplies from a spring between the two, but nearer _B_. During the
summer previous to this outbreak a gang of Italian laborers, engaged in
double-tracking the Central New England Railroad, were housed in box
cars standing on one track of the railroad. One of the members of the
gang was reported to have been taken ill with a fever and was at once
removed, it was supposed, to a hospital in New York. It was the practice
of the Italian laborers to bathe and wash their clothes in the upper of
the two ponds from which water is supplied to the creamery by the pipe
line. All the persons who contracted the fever were supplied with milk
from the creamery. The foreman, who was the first to contract the fever,
used water from the creamery and from the well at the house where he
boarded. The other families, as already mentioned, used water from the
spring. The conclusions, therefore, are that the creamery in some way
became infected with typhoid fever, probably through the water-supply
from the pond, and that the first two cases were due directly to this
cause; that the station agent and his wife contracted the fever because
of the infection of the spring, either from some small stream which is
the outlet of the ponds or from some infection due to the illness of the
owner of the house _B_ near by. The report concludes as follows: "The
use of water for creamery purposes from a pond exposed to such
unwarranted and unchecked pollution as is shown here, or the permitted
abuse of a water-supply for a creamery, appears little less than
criminal negligence on the part of those responsible for the management
of the creamery."
[Illustration: FIG. 37.--Contamination of a creamery from the
water-supply.]
Another report in this volume of the New York State Department of Health
illustrates very well how a spring or well may be contaminated, and is
taken from a report on an outbreak at Kerhonkson, Ulster County. The
report reads as follows: "The village of Kerhonkson is built mainly on
the side of a mountain of solid rock covered by a thin top soil of
variable depth. Owing to its rocky nature, only one or two wells exist
throughout the whole place; such a thing as a drilled well has never
been seriously considered.
"The inhabitants obtain their drinking water from a well on the property
adjacent to and above the present school building, and known as the
"Brown" well, and from a clear spring at the bottom of the hill in the
rear of the village store and known all over the region as the
Loundsbury spring.
"The school building is an old-fashioned two-story ramshackle affair
with overhanging eaves, especially designed to obstruct light and darken
the upper schoolroom. The building is in the center of a pine grove 250
x 150 feet in size, which also obstructs the light and tends to dampen
the building. At the extreme ends of this school lot are two privies for
the boys and girls, built on loose stone foundations, innocent of mortar
or cement, which allows the water in heavy storms to wash out the fecal
contents of from nearly a hundred pupils down upon the habitations
below. Were the wells existing in the village as carelessly constructed
as the Brown well and the various privy vaults which I have inspected,
the loss of life from typhoid fever would be terrible indeed.
"Obtaining the names of all the patients who had suffered from this
disease, I found that all but three were Kerhonkson public school
pupils, and all had drunk the water of the before-mentioned well on the
Brown property. Two out of these three cases were mothers of pupils who
had been stricken with the fever and who had nursed the children through
their long and exhausting illnesses and afterward had been attacked by
the disease themselves, while the third and remaining case was a
puzzler. This boy had never been a pupil of the school in question, nor
had he partaken of any of the water of the suspected well. He was a
pupil of another school entirely and lived in an adjoining village a
considerable distance away. A special visit to him, however, developed
the fact that some time before his illness he had come to the village
store in Kerhonkson to purchase goods and had drunk water from the
Loundsbury spring.
"Two years ago two cases died of typhoid fever on the property on which
the Brown well is situated. Their stools were treated with lime and
buried on the hill behind the house. Three cases of the same fever have
occurred in the same house this season. The well in question is laid up
with stone and cement and was supposed to be tight and impervious to
surface water contamination. Investigation, however, proved that there
were openings in the stone work in the side toward the privy. On
examining the privy it was found that the foundation was composed of
loose stones without cement or mortar that would readily allow the fecal
contents to be washed down toward the well, the privy being about three
feet higher than the well, the natural descent of the land being about
one foot in twenty-five, the distance between privy and well being only
about eighty feet. Another factor favoring the well contamination from
this privy is that any filth washed downward from the privy toward the
well would be stopped by the wall of the house proper and carried
directly toward the well which lies close to the southeast corner of the
house. Thus all of the conditions point to privy contamination of this
well which should be at once cemented up on the inside, thoroughly
cleansed and purified, before its use should be permitted, while all the
privies in question should be provided with vaults of brick eight inches
thick with eight-inch brick floors all laid with cement, and their
inside surfaces lined with cement at least one inch thick, to prevent
any further possible contamination."
In view of the imminent danger always possible wherever human wastes are
directly discharged into streams, whether from privies or sewers, it is
obvious that water so contaminated should never on any account be used
as drinking water. It does not follow, because a stream so contaminated
has been used for months or years without producing any evidence of
disease, that the water is safe. Unless an excessive amount of organic
matter is so transmitted, no evidence will be found that such pollution
has existed through any outbreak of disease. But if once the discharges
become affected through a person having typhoid fever, then the result
of the infection is apparent immediately. If, therefore, an inspection
of the stream above the point where it is proposed to take the
water-supply shows the existence of privies, as shown by Fig. 36, the
water should not be used for domestic supply, although a number of
individuals may have been using the water for years without bad effects.
It is a case in which prevention is much wiser than cure, and while
economy and convenience may indicate such a polluted stream to be a
desirable source of supply, a proper regard for health conditions will
rule it out absolutely.