WATER.
=Uses of Water.=—Water is a prime necessity of life. In its absence
life can only exist in lowly organised beings, and in them only in
a dormant state. From a hygienic point of view, the uses of water
are four-fold:—(1) It is =an essential part of our food=, not only
serving to build up the tissues of the body, but also preserving the
fluidity of the blood and aiding excretion of effete matters. (2)
It is necessary for =personal cleanliness=, of which the importance
can scarcely be exaggerated. (3) =In the household= it is essential
for cooking, as well as for washing the house, the linen, and
various utensils. (4) By =the community at large= it is required
for water-closets and sewers, for public baths, for cleansing the
streets, and for horses and other domestic animals, as well as in
many manufacturing processes. It is obvious that the water to be used
for domestic and general purposes, need not be so pure as that for
drinking purposes. Hence, a double supply was proposed for London in
1878, by the Metropolitan Board of Works—a less pure river supply for
general purposes, and a deep chalk-well supply for drinking purposes.
The scheme, however, rightly fell through, because of the expense of a
double source of supply, and the danger that the impure water would,
through carelessness or ignorance, be often used for drinking purposes,
when it happened to be nearest at hand.
=Quantity of Water Required.=—The quantity of water required for all
purposes has been variously stated by different authorities. The
quantity required for drinking purposes is found to bear a relation
to the weight of the individual, being nearly half an ounce for every
pound weight, or 1½ gills for every stone weight. Thus, a man
weighing 150 lbs. would require 3-3∕4 pints. Of this water, about
one-third is taken in the food; the remainder, averaging 2½ pints,
being required as drink. If we add the water required for other
purposes, according to De Chaumont, 1 gallon is required for drinking
and cooking, 2 gallons (not including a bath) for personal cleanliness,
3 gallons for a share of utensil and house washing, 3 gallons for
clothes washing; and if a general bath be taken, 3 gallons more; making
a total of about 12 gallons, to which 5 gallons must be added if there
is a water closet.
In hot summer weather the consumption is about 20 per cent. above the
average of the year; and frost often increases the amount 30—40 per
cent. above the average, owing to the bursting of pipes, or the loss
from taps foolishly left open to prevent bursting.
Water companies usually reckon 30-60 gallons for each individual, to
allow for the water required for scavenging and manufactories and for
waste. In large houses and hotels where baths are freely used, often
as much as 70 gallons per head is used, and in hospitals the amount
averages from 60 to 90 gallons per head. The following is Parkes’
estimate of the daily allowance for all purposes:—
┌─────────────────────────┬────────────────┐
│ │GALLONS PER HEAD│
│ │ OF POPULATION. │
│ ├────────────────┤
│_Domestic supply_ │ 12 │
│_General baths_ │ 4 │
│_Water-closets_ │ 6 │
│_Unavoidable waste_ │ 3 │
│ │ ── │
│ _Total house supply_ │ 25 │
│ _Municipal purposes_ │ 5 │
│ _Trade purposes_ │ 5 │
│ │ ── │
│ _Total_ │ 35 │
└─────────────────────────┴────────────────┘
It has been proposed to put a water-meter to each house, so that the
rate may be in proportion to the amount of water used. The plan is
objectionable for two reasons: 1st—Because it tends to restrict the
necessary use of water for purposes of cleanliness. A scant supply of
water is always followed by uncleanliness of house and person, with
its consequent diseases; at the same time closets may be imperfectly
flushed, and may become choked. 2nd—Because of the primary expense of
the meter, and of its maintenance.
SOURCES OF WATER SUPPLY.—All our drinking water is obtained in the
first instance, by a natural process of distillation on a large scale.
The sun is constantly causing evaporation from sea and land. The vapour
produced, being condensed by a lower temperature, returns to the earth
as snow, dew or rain. All these natural products have been at times
utilised as sources of drinking water.
1. =Dew= has on rare occasions been utilised at sea by hanging out
fleeces of wool at night and wringing them out in the morning. A much
better plan is—
2. The =Distillation of Sea-water=. This can easily be managed now that
steam power is so largely used. It has even been employed on land, when
it was necessary temporarily to continue the use of water derived from
an impure source. The first part distilled should always be rejected,
as it is always impure. Distilled water is “flat” in taste, owing
to its containing no dissolved gases. It can be aërated by letting
it drop a considerable distance from one cask into another, through
small openings in the upper one, and by filtration through charcoal.
Non-aërated water is not easily absorbed into the circulation, and
occasionally causes illness.
3. The utility of =Melted Snow and Ice is= obviously very limited.
Moreover, its use is not free from danger if the ice is derived from
contaminated water. Outbreaks of enteric fever have been traced in the
United States to the taking of ice obtained from impure water.
4. =Rain-water= is a much more important source of water supply, and
after passing through the soil it constitutes the chief part of the
water we drink. The term, however, is properly restricted to the water
collected immediately after its descent from roofs, etc. Its purity
depends on three conditions—the character of the air it passes through,
the cleanliness of and absence of lead from the channels through which
it runs, and the condition of the water-butts in which it is stored.
Rain-water is soft; in fact, too soft to be pleasant to the palate. In
passing through the air, it carries with it a certain proportion of its
constituents; in towns especially ammonia, soot, etc.; near the sea,
it generally contains some salt; and being soft and having dissolved
oxygen from the air, it dissolves an appreciable amount of lead from
roofs or gutters.
The Rivers Pollution Commissioners found that out of eight samples
of stored rain-water only one was fit to drink. They came to the
conclusion that rain-water, collected from the roofs of houses and
stored in underground tanks, is “often polluted to a dangerous extent
by excrementitious matters, and is rarely of sufficiently good quality
to be used for domestic purposes with safety.” Also, that in Great
Britain, and more particularly in England, we shall “look in vain to
the atmosphere for a supply of water pure enough for dietetic purposes.”
The use of rain-water for drinking purposes is only justified in
isolated country houses where no better source is available; and under
these circumstances the greatest care should be taken to prevent
contamination with lead or organic impurities.
The amount of water falling on any impervious material obtainable from
rain can easily be estimated, if the amount of rainfall and the area of
the receiving surface are known. The average annual rainfall in this
country is 33 inches (see page 236).
We may assume the amount practically available to be 20 inches per
annum, and the area of the receiving surface 500 square feet. Multiply
the area by 144, to bring it into square inches, and this by the
rainfall, and the product gives the number of cubic inches of rain
which fall on the receiving area in a year. One cubic foot, or 1,728
cubic inches, of water being equivalent to 6·23 gallons, the number of
gallons of water can be easily calculated. To calculate the receiving
surface of the roof of a house, do not take into account the slope of
the roof, but merely ascertain the area of the flat space actually
covered by the roof. This may be done roughly by calculating the area
of all the rooms on the ground floor, and allowing an additional
amount for the space occupied by the walls. It has been estimated
that, even if a rain-water supply for towns were desirable, the amount
collected from the roofs of houses would scarcely average two gallons
per person daily—assuming the average rainfall to be 20 inches, and
that there was a roof area of 60 square feet for each individual.
The amount practically available from rain falling on different soils
varies with their porosity and slope. Thus, according to Professor
Rankine, the proportion of the total rainfall available is as follows:—
Nearly the whole on steep surfaces of granite, gneiss, and slate;
From three to four-fifths on moorland hilly pastures;
From two-fifths to half on flat cultivated country; and
None on chalk.
By available rainfall is meant the amount remaining after allowing for
percolation, etc., which can be stored in reservoirs.
5. =Upland Surface Water= is the water collected in hilly districts, as
on moorlands, at the head of a river. By its utilisation for drinking
purposes, the sources of water for the river are interfered with, and
any water company or local authority using such a source is, therefore,
required to run into the stream a quantity of water equal to a third of
the available rainfall. The limited and regular supply thus furnished
to the stream is found to be advantageous for industrial purposes as
its flow is equalised, and the violence of floods mitigated.
In the utilization of upland surface water the water from the
surrounding hills is collected at the bottom of a valley, in an
artificial, strongly-constructed lake; or in a natural lake, as in Loch
Katrine (from which Glasgow is now supplied).
Upland surface water is nearly always soft. Its use is much more
economical than that of hard water. It may be brownish, from the
presence of peat, but this is not objectionable, so far as health is
concerned. Its occasionally solvent action on lead is a more serious
objection. The population of many parts of Yorkshire and Lancashire
have suffered severely from chronic lead poisoning, due to the action
of certain upland surface water on lead service pipes. Only the waters
giving an acid reaction possess this plumbo-solvent power. (See also
page 82.)
6. =Springs= supply water which, originally derived from rain-water,
has percolated through the soil until it reaches some impervious
stratum, and has then run along this, until it arrives at the point at
which the impervious stratum reaches the surface of the soil. A spring
is thus the outcrop of the underground water. Springs are divided into
(1) land springs, and (2) main springs. The former flow from beds of
drift or gravel lying on an impervious stratum. They are very subject
to seasonal variation, and may dry up in certain years; while main
springs occurring in chalk, greensand, or other regular geological
formation, constantly supply a certain amount of water. Springs often
occur in connection with “faults” in geological strata, and then may
appear on table-lands and high elevations, unlike springs caused by
alternation of strata in valleys of denudation. The two kinds of
springs are shewn in Fig. 5 and 6.
In the land spring water crops out at the point where the porous
stratum ceases. Deep springs may crop out in the same way as land
springs, except that they appear at the bottom of deeper strata. Or
they may be formed by faults. Both these are shown in water having
percolated through the chalk beneath the superficial clay, is stopped
at the “fault” by the lack of continuity of the chalk stratum, and is
consequently confined under pressure. It therefore makes its way to the
surface, forming a spring. In its passage underground, water (owing
partly to the carbonic acid it has obtained from the air and soil), is
able to dissolve small quantities of chalk, sulphate of lime and of
magnesium, and traces of oxide of iron, aluminium oxide, and silica.
Spring-water possesses an equable temperature, generally about 50°
Fahr., while impounded or river water is always warm in summer and cold
in winter. Spring water is well-aerated, while river water, and still
more rain-water, are flat.
[Illustration: FIG. 5.—LAND SPRING.]
[Illustration: FIG. 6.
MAIN SPRINGS FORMED IN VALLEY OF DENUDATION AND BY A FAULT.]
7. =Wells= may form the best or worst sources of water-supply according
to their depth and the means of protection against contamination. There
are two kinds—_Surface wells_ and _deep wells_.
=Surface Wells= do not usually descend further than 15 or 20 feet,
and have no impervious stratum between the source of water and the
surface of the well. They catch the subsoil or underground-water, which
percolates into them from the surrounding soil, and the character of
the water they receive will therefore vary with the nature of their
surroundings. If there is a cesspool near, this may simply drain into
the well. All the soakage from a considerable distance may find its way
into the well. In villages and isolated places the water of surface
wells is commonly contaminated. One hole may be dug in the garden for
a well, and another for a cesspool, while there is possibly a farmyard
near at hand—the soakage from the cesspool and farmyard soaking into
the well. Danger may also arise from more distant contamination. The
ground water which is tapped by the well is an underground stream
flowing towards the nearest brook. Heavy rains swelling the ground
water may wash impurities from cesspools, leaky drains, etc., at
a considerable distance, and carry these into wells lying between
these sources of pollution and the brook into the bed of which the
underground water ultimately discharges. The danger of contamination of
the water in the well by the contents of the cesspool is much greater
in the relative position shown in A than in the position shown at B,
Fig. 7. After heavy rain, when the underground water is swollen, the
danger of contamination is still further increased. The model bye-laws
of the Local Government Board state that a cesspool must be at least
40 feet distant from any well, spring, or stream. Probably this is
insufficient for safety; cesspools ought to be entirely forbidden. If
necessary to retain a surface well, it should be protected nearly to
the bottom with brick, lined with an impervious layer of cement so as
to prevent water from entering the well except near its bottom. In
modern wells iron cylinders are employed to line the upper part of the
well; and large glazed earthenware pipes arranged vertically and with
water-tight joints are sometimes used for the same purpose.
[Illustration: FIG. 7.
SHOWING VARYING DANGER OF CONTAMINATION OF A SHALLOW WELL, ACCORDING TO
LEVEL OF UNDERGROUND WATER AND RELATIVE POSITION OF CESSPOOL AND WELL
(_after Galton_).]
=Deep Wells= are made by digging a surface well, as above, except
that the ground water is prevented from entering the well by means of
impervious steining; and then boring from the bottom down through the
subjacent impervious stratum until a water-bearing stratum is reached.
The difference between a surface well and a deep well is shown in
Fig. 8 by A and B. Where the water in this stratum is retained under
pressure, deep wells are known as =Artesian Wells=. Such Artesian wells
have been sunk in London. Rain, falling on the chalk hills which lie to
the south and north of London, percolates through the chalk downwards,
and then laterally, until it lies in the concave London basin. Here the
clay stratum above it prevents its escape upwards; and being confined
under considerable pressure, it rises to the surface, or into a well
in the superficial gravel, when the clay is tapped. In Fig. 8, B is an
Artesian well if the pressure is such as to make the water rise through
the London clay, when this is cut through and the underlying chalk
is reached. C is a well in the chalk, which does not pass through an
impervious stratum, and therefore comes within the above definition of
a surface well; but as regards depth required to be dug before water is
reached it is more like a deep well.
[Illustration: FIG. 8.
SHOWING DIFFERENCE BETWEEN DEEP AND SUPERFICIAL WELL. _A._—SURFACE WELL
IN GRAVEL. _B._—DEEP WELL, GOING THROUGH GRAVEL AND CLAY TO CHALK.
_C._—WELL IN CHALK DISTRICT.]
Among the deepest Artesian wells are Grenelle (1,800 feet), and
Kissingen (1,878 feet.) The sinking of a deep well and severe pumping
of its water may exhaust all the neighbouring wells for two or three
miles. There is also danger of contamination from neighbouring
cesspools when the upper part of the deep well is not properly
constructed. The area exhausted by a deep well undergoing pumping is
represented by an inverted cone, having a very wide base, and with a
convex inner surface pointing towards the well.
For country places deep-well water is much preferable to water from
streams, as streams are very liable to be contaminated by the sewage
of houses higher up in their course, or even by that of houses close
by. A good well should be at least thirty feet deep—preferably fifty
feet and should always be lined with impervious material, except near
its bottom. The absolutely water-tight and impervious condition as well
as the distance of all drains or cesspools in the vicinity should be
ascertained before deciding whether the drinking water from a given
well is above suspicion. The direction of flow of the underground water
should also be determined. This may be done by measuring the level of
all the wells in the neighbourhood. Possible sources of pollution at
points from which ground water is flowing towards the well are much
more dangerous than those nearer than the well to the river towards
which the underground water is flowing (see Fig. 7). Steam pumping
greatly increases the area from which contamination may be derived.
An excellent plan to obtain water for villages, in a gravelly soil, is
to sink a Norton’s Abyssinian tube well for fifty or sixty feet.
In towns it is preferable to trust to the public water supplied, rather
than to any private well; and in villages, a general supply from a pure
source should also be provided.
The water is obtained from a well by a _pump_ or a _draw-well_. The
former is a safer as well as a less laborious plan. The pump should be
fixed some distance from the well, and the aperture through which the
pump pipe passes should be rendered water tight. Lead pipes should be
avoided, as well water not infrequently has plumbo-solvent properties.
8. =Rivers= and running streams originate in upland surface water
or springs, and their water should be of the same quality as these.
Unfortunately, they acquire a large amount of impurities in their
course. Towns commonly pour their more or less clarified sewage into
them; and the discharge of crude sewage from hamlets and single
houses on the banks is still far from uncommon. With the more rigid
enforcement of the Rivers Pollution Acts, this pollution of rivers
will become less frequent; but river water previously contaminated by
even small amounts of sewage cannot be regarded as an ideal source of
water-supply.
If no contamination be present in the water of a river, it forms a good
source of water-supply; being running water, it is always fairly well
aërated, and is not usually so hard as spring-water.
Even if sewage has entered a river, it is asserted that it becomes a
safe source of water-supply, after passage through filter beds, the
sewage having been got rid of in four ways.
1st.—By _subsidence_, the organic matter settling to the bottom.
2nd.—By the influence of _water-plants_, which assimilate ammonia,
nitrates, etc., and give out nascent oxygen.
3rd.—_Oxidation._ Doubtless a large amount of the nitrogenous matter
does become oxidised in its course down a river, and in this condition
is harmless. The river Seine becomes greatly polluted as it passes
through Paris, but so far as chemical analysis can determine its
condition, it is purer 30 miles below the city than it was before it
received the sewage of the city.
4th.—It is highly probable that the germs (or micro-organisms) of
enteric fever and other diseases known to be propagated by polluted
water, are practically or wholly destroyed in the struggle for
existence with the natural micro-organisms of river-water. When to
this is added the fact that river-water supplied to large communities
is carefully filtered through sand, after having been stored in
reservoirs, in which the chief impurities have time to settle, it is
not surprising that the experience of those communities like London,
which are supplied with river-water, usually shows no evidence of evil
ascribable to drinking this water. For over 30 years the inhabitants
of London have been drinking filtered water from the river Lea and
from the Thames above Teddington, and this gigantic experiment on a
population which has increased from 2½ to 5 millions has not been
accompanied by any conclusive evidence of evil effect.
In regard to the comparative merits of the various waters described,
it will be useful to give here the classification made by the Rivers
Pollution Commissioners in their sixth report:—
{ . Spring Water }_Very palatable_.
_Wholesome_ {2. Deep-well Water }
{3. Upland Surface Water }
}_Moderately palatable_.
{4. Stored Rain Water }
_Suspicious_ {5. Surface Water from Cultivated }
{ Land }
}_Palatable_.
{6. River Water to which Sewage gains }
_Dangerous_ { access }
{ 7. Shallow-well Water }
Passage through certain geological strata has a great influence in
rendering water palatable, colourless, and wholesome by percolation.
The following strata are said by the Commissioners to be the most
efficient:—(1) Chalk, (2) oolite, (3) greensand, (4) Hastings sand, (5)
new red and conglomerate sandstone. Fissures or cracks in these strata
may cause the water to pass through them unpurified by filtration.