1 Translated by J. A. Ball, Esq., aud published by the Local Govern-
meut Board.
Digitized by
Google
THE INTERPRETATION OF WATER ANALYSES 191
micro-organisms in a cubic centimetre as open to suspicion ;
but, as we have just seen, he does not regard such water, if
once polluted, as absolutely safe, however careful and thorough
the filtration ; but to this question we shall have shortly
to refer again. The Royal Commissioners on Metropolitan
Water Supply do not entirely concur with this conclusion.
They point out that the typhoid bacillus is, so far as is
known, only found in human excrement, and that it has
not yet been found to retain its vitality when in faecal matter
for more than 15 days; that in all ordinary waters there
exist organisms which "undoubtedly exert an influence
in diminishing the vitality of the typhoid bacillus ; that
exposure to direct sunlight destroys these bacteria; that
they have a tendency to subside more or less rapidly in all
slowly-moving waters, and to be carried down with other
matters held in suspension ; and that there are strong grounds
for believing that small doses either of cholera or of typhoid
poison may be swallowed with impunity. Such being the
case, they fall back upon the " evidence of experience," and
whilst acknowledging that the various water supplies to
London are contaminated with sewage, which may, and often
does, contain the specific poison of typhoid fever, and may
contain the bacillus of Asiatic cholera, they "state without
hesitation, that, as regards the diseases in question, which
are the only ones known to be disseminated by water, there
is no evidence that the water supplied to the consumers
in London by the companies is not perfectly wholesome."
In other words, these polluted river waters, which have under-
gone a filtration far less perfect than that required by Koch
(since London water usually contains many hundreds of
micro-organisms in the cubic centimetre), are perfectly safe
and wholesome.
The attempt to set up a standard of purity based upon the
number of micro-organisms in a given quantity is as illogical
as the old chemical standards. Both depend upon quantity,
whilst the real point at issue is the quality. In reputedly
Digitized by
Google
1 92 WATER SUPPLIES
good waters it has been observed that the micro-organisms
present capable of liquefying gelatine by their growth are
few in number, whilst in sewage-polluted waters they abound ;
but this fact is of little value, since it only enables somewhat
gross pollution to be detected, and most of these liquefying
organisms are perfectly harmless. Bacteriology, like chemistry,
may tell us something of hazard and impurity, but neither can
be depended upon to determine with certainty whether a water
is actually injurious to health. To condemn one water
because it yields a little more albumenoid ammonia than
another, or because it contains a few more organisms than
another, when we know nothing of the nature of the sub-
stance yielding the ammonia, and nothing of the character of
the organisms, is obviously so illogical as to be absurd, and
yet this is what is almost invariably done. Bacteriological,
microscopical, and chemical examinations must always be
associated with a thorough investigation of the source of the
water, to ascertain the possibility of contamination, continuous
or intermittent. Then, and then only, if everything be satis-
factory, we may be justified in speaking of safety and of
freedom from risk; but where either the bacteriological,
microscopical, or chemical examination is unsatisfactory, the
inquiry into the history of the water must be most careful
and complete, and a guardedly-expressed opinion given only
after a full consideration of the bearing of the one upon the
other. The possibility of accidental pollution is a point
too often overlooked; yet it is to such accidental pollution
that outbreaks of disease are most frequently attributed, and
of this the examination of samples of water, prior to the
occurrence of the contamination, may tell us little or nothing.
The danger of such pollution does not, unfortunately, vary
with the amount of any constituent found in the water, and
a source yielding a water of great chemical and bacterial
purity may be more liable to occasional fouling than a source
yielding water containing excessive quantities of chlorides
and nitrates, or even of unoxidised organic matter.
Digitized by
Google
CHAPTER XI
THE POLLUTION OF DRINKING WATER
In the preceding chapters many illustrations will be found
of the ways in which water may become polluted; and in
the succeeding chapters frequent reference will have to be
made to the subject; yet it appears advisable to consider it here
somewhat systematically, since it forms a natural supplement
to the two preceding sections. From what has been already
said it is evident that by far the most dangerous polluting
matters which can gain access to a drinking water are the
solid and liquid waste products cast out of the human system
and usually deposited in cesspits, cesspools, drains, and
sewers. There is a widespread and very erroneous impression
that in districts without water-closets the drainage, consisting
merely of slop water, is practically innocuous, and that it
may be disposed of in ways not admissible with ordinary
sewage. Chemically and bacteriologically, it is almost im-
possible to distinguish between the sewage of towns in which
water-closets are in general use, and of towns in which other
forms of excrement collection and disposal are adopted. In
the drainage from the former we have all the chamber slops,
the water in which soiled bed-linen, clothing, etc., have been
washed; and both these are not only excessively foul, but
may also be specifically polluted. Both kinds of sewage,
therefore, must always be dangerous ; and every effort
should be made to prevent their gaining access to any
source of water supply. '
o
Digitized by
Google
194 WATER SUPPLIES
Pollution of Water at its Source.
(a) Rain and Rain Water. — Rain water, if collected with
ordinary care, is never likely to be polluted with human
excrement. It frequently contains the ordure of birds, soot,
dust, and decaying vegetable matters, which have accumu-
lated during the dry weather on the collecting area, and
all of which are more or less objectionable; but I know
of no instance in which the use of such rain water has
caused disease (vide Chapter II.). These constituents usu-
ally render the water so unsightly and unpalatable that no
one will use it until after it has been filtered or boiled ; and
this may account for the absence of any deleterious effects.
Such rain water, when kept, appears to undergo some
process of fermentation and self -purification, which renders it
again bright and fairly palatable. When collected by aid of a
"separator," so as to prevent the first washings of the roof or
other collecting surface passing into the reservoir or tank,
and when properly stored, the rain furnishes probably the
safest of all waters for drinking purposes.
(b) Surface and River Waters. — Water collected from un-
inhabited moorland or mountainous districts may contain
vegetable matter, but will be free from animal pollution.
If from cultivated land, manurial matters, more or less
changed by oxidation, will gain access to the water. As
human excrement is constantly employed as manure, the
pollution may be of a dangerous character. In such districts
also there must be human habitations, farmyards, etc. ; and
unless special precautions are taken, the drainage from these
will contaminate the water. Cesspits and cesspools are
frequently so defectively constructed as to permit of the
contents being washed out by heavy rains; or they may-
overflow into ditches, and the filth be carried into the
nearest watercourse. During dry seasons such streams may
receive but little polluting matter, whilst in seasons of flood
the accumulated filth of months may be carried into them.
Digitized by
Google
THE POLLUTION OF DRINKING WATER 195
In too many instances the whole of the sewage of towns is
discharged bodily into rivers which are used a few miles
lower down as the water supply to other towns and villages.
No doubt in the course of transit from point to point much
of the solid matter is deposited on the sides and bottom of
the river, and some of the dissolved filth is oxidised or
otherwise destroyed ; but it is open to question whether any
river in this country is sufficiently long for this process of
self-purification to be complete, and for the water to become
absolutely free from danger. With every flood the deposited
filth is disturbed and carried downwards; and unless due
provision has been made for tiding over these periods without
having to abstract the turbid water, seriously-polluted water
may have to be used, and if the filtration be not perfect,
serious consequences may ensue. Many outbreaks of typhoid
fever have been attributed to the use of such waters. For
long periods the consumption of the water may have produced
no injurious effects ; but an exceptional flood or the failure
of a filter bed at a critical period may result in a serious
outbreak of disease. Examples of epidemics so produced
have already been referred to. No doubt the danger arising
from the introduction of sewage into a stream supplying
drinking water varies with the proportion of sewage to the
volume of water into which it is discharged; but, however
small this proportion, it cannot be said that the degree of
dilution is sufficient to render the water entirely safe. When
sewage has been purified by chemical treatment or by fil-
tration through land, doubtless the danger is reduced to a
minimum, but there is always the risk of imperfectly-
purified sewage being carried into the stream. That the
effluent from a sewage farm may pollute a drinking water
in such a way as to cause disease seems probable from the
report on the outbreak of typhoid fever at Beverley already
mentioned. It is true that in this case the water contaminated
was derived from a well ; but had the effluent found its way
into a stream used as a water supply, it is not improbable
Digitized by
Google
196 WATER SUPPLIES
that the result would have been the same (vide Chapter XII.,
on the " Self-purification of Rivers ").
(c) Subsoil Water. — In thinly-populated districts the sub-
soil water may be absolutely free from any trace of sewage
contamination. In populous districts, on the other hand, a
considerable amount of sewage must gain access to the subsoil.
Fortunately, however, the " living " earth possesses such puri-
fying properties that the filth may be rendered perfectly
powerless for evil. In fact, Koch has given it as his opinion
that " the subsoil water gives us absolute security with respect
to the danger of infection, and it should, therefore, if it can
only be obtained in sufficient quantity, and if it is not objected
to on account of chemical characteristics, e.g. too great
hardness, or too great an admixture of chloride, be preferred
under all circumstances to surface water. I indeed hold it
even to be desirable, and in some cases even necessary, that
works already constructed to filter river water should be so
changed as to be used for obtaining subsoil water." As most
subsoil waters have received an admixture of sewage, how is
it that such a careful observer as Koch can regard it as under
all circumstances preferable to surface water? The fertility
of soil depends upon the presence of organic matter, vegetable
or animal, undergoing decay. This decay is almost entirely
due to the action of micro-organisms, which produce nitric
and carbonic acids, without the former of which the soil
would be practically barren. The decomposition of organic
matter appears to take place in three stages. First, ammonia
is produced, and this probably by the action of several species
of bacteria ; next, the ammonia is converted into nitrous acid
by an organism discovered simultaneously in 1890 by Frank-
land and Winogradsky; finally, another organism has been
proved by Warington and Winogradsky to be the cause of
the conversion of the nitrous into nitric acid. In rainless
districts nitrates accumulate upon the surface, immense
deposits being found in Chili, Peru, and various parts of
India. In other regions the nitrates so formed are dissolved
Digitized by
Google
THE POLLUTION OF DRINKING WATER 197
by the rain and carried to the roots of plants, and serve for
their nourishment. The projwrtion not so utilised by plants
as food passes into the subsoil water. All the organisms
above referred to are found most abundantly in the first few
inches of soil, the numbers decreasing rapidly with the depth,
until at a few feet from the surface they are no longer to bo
detected. Where the surface is covered with vegetation, the
decomposition of dead organic matters is so complete, and
the amount of nitrate extracted so large, that no undecomposed
organic matter and little of the products of its decay reaches
the subsoil water. Moreover the undisturbed soil constitutes
one of the most perfect of filters ; hence subsoil water, if properly
collected, is one of the purest of waters, providing the mineral
ingredients of the subsoil are not too soluble, or are not of
an otherwise objectionable character. In towns and villages
where there are aggregations of houses, or even in the prox-
imity to single cottages, the surface soil may be so denuded
of vegetation that this process of decomposition may not be
complete, and unchanged or only partially changed filth may
be washed through into the ground water. Where the filth
escapes from defective drains, cesspools, and cesspits, this is
still more likely to be the case ; hence water obtained from
wells in proximity to such defective sanitary arrangements
must be polluted. In towns and villages, especially where
such defects are common, the whole of the subsoil water over
a large area may be contaminated. Doubtless, even here
the filtering powers of the earth are most marked, otherwise
outbreaks of disease would be much more frequent amongst
communities using such water; but the records of every
medical officer of health prove that this filtration cannot
always be depended upon to remove the germs of disease.
A heavy rainfall, either by carrying the filth through with
unusual rapidity, or by causing the ground water to rise into
the more polluted soil above, may carry these organisms into
the wells, and so produce an epidemic. Where wells are
improperly constructed and allow of water entering at or near
Digitized by
Google
198 WATER SUPPLIES
the surface, the danger is greatly accentuated. Where they
are open at the ground surface, or where the covering is
defective, heavy rains may wash the filth directly into the
water. The great difficulty experienced in constructing wells
so as to exclude impure surface water leads Koch to conclude
that "Wells, constructed no matter how, should not be
tolerated in future" (vide Chapter IV.). Koch's remarks,
therefore, do not apply to ground water as derived from wells
of any kind. It must also be remembered that where the
subsoil is full of fissures, impurities may be carried along
such channels for considerable distances and contaminate the
drinking water at a point far from where the polluting matter
enters the ground. Thus the epidemic of typhoid fever at
New Herrington was proved to be due to the drainage from
a farm three-quarters of a mile away from the well, the
channel of intercommunication being undoubtedly the fissures
in the rock forming the subsoil.
The natural level of water in a shallow well is that of the
plane of saturation of the subsoil, A, C. When the level of the
water in the well is lowered by pumping, an area of ground
around is drained, the extent of this area depending upon
the porosity of the soil and the depth to which the water is
abstracted. The ground drained has the form of an inverted
cone, with a rapidly-increasing gradient towards the well, E
(Fig. 13). The drainage area has been found by experi-
ment to have a radius ranging from 15 to 160 times that
of the depression due to pumping ; hence polluting matters
gaining access to the subsoil within this area will flow into
the well. The extent of the drainage area varies with the
porosity of the soil ; where the soil is dense and but slightly
pervious the area may not exceed 15 times the depth of the
water in the well when at its highest level, whereas where
the subsoil is exceedingly porous the area may be 160 times
this depth. As in most cases the subsoil water is travelling in
a definite direction, if the point of pollution, B, be where the
plane of saturation is higher than that around the well, and
Digitized by
Google
THE POLLUTION OF DRINKLNG WATER 199
the latter is in the line of flow of the subsoil water from
where the pollution enters, it is tolerably certain to gain
access to the well, either continuously or occasionally, when
the level of the ground water rises above a certain height.
If the sewage or other polluting matters enter the subsoil at
the other side of the well, the risk of contamination is greatly
Fig. 13.
diminished. Hence in districts where the ground water is
polluted locally the position of the well is of considerable
importance.
The prevalence of malarial diseases, enteric fever, and
cholera is believed by many sanitarians to be influenced
largely by the rise and fall of the ground water. Frequently,
in India, outbreaks of malaria have followed a rapid rise in
the ground water, due to heavy rainfalls, and the epidemics
may have been due to the contamination of the wells by the
filth carried down by the rain. Pettenkofer, at Munich,
Digitized by
Google
200 WATER SUPPLIES
found that enteric fever was most fatal when the subsoil
water was lowest, and especially when the fall had been rapid
and from an unusual height. Fodor, at Buda-Pesth, found
exactly the opposite condition to obtain, the enteric fever
mortality rising and falling with the ground water ; and this
connection between the height of the subsoil water and the
prevalence of enteric fever ha3 been observed from time to
time in this country. Where this has occurred, the explana-
tion which suggests itself is, that the water became more
and more polluted with the rise in level, and this is the
generally -accepted opinion in this country; but there are
many eminent observers both here and on the continent who
do not accept this explanation. Pettenkofer also regards
cholera as a disease, the spread of which is largely influenced
by the movements of the subsoil water. Even if such is the
case, which is by no means generally admitted, it may be
that the effect is due rather to the varying extent to which
the water becomes polluted, rather than to the fouling of the
ground air by the decomposition of the organic matter and
the active growth of specific organisms in the damp soil left
by the falling ground-water.
Springs fed by subsoil water will be affected in quality in
the same way as the water in wells, but only rarely to the
same extent. Such springs usually drain considerable areas,
and therefore, unless the pollution arises near the source of
the spring, the dilution will be great, and during the period
which must elapse between the impurity entering the ground
and its reaching the outlet, time will have been allowed for a
more or less complete oxidation of the organic matter in the
pores of the soil, and for a more or less complete filtration to
have occurred. Baldwin Latham found that at Croydon,
which is supplied with water from springs in the chalk, measles,
whooping-cough, and diphtheria were more prevalent during
wet seasons, when the ground-water level was high, and that
typhoid fever and small-pox were liable to become epidemic
when heavy rains followed a prolonged drought. In rural
Digitized by
Google
THE POLLUTION OF DRINKING WATER 201
districts springs are frequently fouled by cattle, and by the
rainfall, if heavy, washing filth into the dipping places, since
the springs are not properly protected. Land springs, fed by
thin beds of sand, or gravel, or light porous soil of any kind,
are especially liable to be seriously affected by manure spread
upon the surface of the ground, and if this manure contain
human excrement the danger is greatly enhanced. In a
recent outbreak of typhoid fever which I investigated, and
which affected a small group of cottages, I found that the
excreta from a mild case of this fever had been discharged
into a defective privy cesspit sunk in the porous soil within
a few feet of the land spring which supplied the cottages.
When slop water, the contents of earth closets, etc., are
properly disposed of by spreading upon a sufficiently large area
of garden or other cultivated ground, the danger of specific
pollution of the ground water is reduced to a minimum.
Where the sewage escapes from defective drains at some
depth from the surface, and excremental filth oozes through
the sides of cesspools and cesspits sunk in the grouud, the
danger of pollution is considerable, and increases with the
proximity of these defects to the point from which the sub-
soil water is abstracted. The model bye-laws of the Local
Government Board require not only that the drains, cesspits,
and cesspools shall be so constructed as to prevent any such
leakage, but also that the two latter shall not be constructed
within a certain distance from "any well, spring, or stream
of water used, or likely to be used, by man for drinking or
domestic purposes, or for manufacturing drinks for the use
of man." Under ordinary circumstances the distance from
a privy should be not less than 40 to 50 feet. Cesspools
being still more dangerous, the minimum distance from a
well should not be less than 60 to 80 feet. Since dust and
debris, when being cast into ashpits, may be blown about, and
so gain access to a well or stream supplying drinking water,
no ashpit should be less than 30 to 40 feet from the
water supply. The proper paving of yards, of pig-styes,
Digitized by
Google
202 WATER SUPPLIES
stables and cowsheds, of slaughter-houses, of business
premises, especially where offensive trades are carried on,
efficient drainage and sewerage, and a proper system of
sewage disposal, are all necessary, not only for preventing the
pollution of the ground water, but also of the ground air, the
condition of the latter being probably as important a factor
in determining the salubrity or otherwise of a locality as the
condition of the former. The burial of the carcasses of
animals near a well may cause pollution of the water, and it
is believed that anthrax may be spread amongst cattle by the
use of water contaminated by the decomposing bodies of
other animals which have died from that disease. The
proximity of a graveyard to a source of water supply is
certainly undesirable; but if the direction of flow of the
ground water be from the well towards the graveyard,
danger will only arise when, by pumping, some of the graves
are brought within the drainage area. If the distance from
the graves to the well be sufficient to exclude the former
from the drainage area of the latter, however heavy and
continuous the pumping required for the supply of water,
there will be little or no danger of contamination from this
source. If, on the other hand, the flow of water be from
the graveyard towards the well, or the well be within
the drainage area above described, the supply will almost
certainly be contaminated. Such waters, and waters from
the neighbourhood of battlefields, have frequently given
rise to dysenteric diarrhcea amongst the populations con-
suming them.
It is well known that the earth around gas mains acquires
an offensive and peculiar odour. Where the mains are
defective this smell is most marked and perceptible at a
great distance from the pipes. It may even reach the
ground water and taint the wells. In 1884 the wells in the
Clarence Victualling Yard at Portsmouth had to be closed on
account of the impregnation of the water with coal gas which
had escaped from the leaky mains traversing the yard. " In
Digitized by
Google
THE POLLUTION OF DRINKING WATER 203
Berlin in 1864, out of 940 public wells, 39 were contamin-
ated by admixture with coal gas" (Parkes).
(d) Deep- Well Water. — The pollution of deep- well water
very frequently arises from defects in the construction of