ORIGIN AND EFFECTS OF THE IMPURITIES OF WATER.
=Origin of Impurities of Water.=—Parkes classifies impurities of water
as:
1. =Those Received at the Source.=—The character of water varies with
the geological structures through which it has passed; with its origin
from the subsoil or cultivated land, or deep wells, or graveyards, or
near the sea, etc. It is a mistaken policy to commence with an impure
water and proceed to purify it; though communities supplied from rivers
may be compelled to submit to this. They must then insist on the most
stringent measures of purification (see p. 96). Inorganic impurities
are of much smaller consequence as regards health than organic; hence
the great advantage of deep well-water over river water. It has been
suggested, however, that when deep well-water becomes polluted, it is
more dangerous than equally polluted river-water, because in the latter
the normal bacteria of water are more abundant, and possibly interfere
with the continued life in water of disease-producing bacteria. This
statement is unproved; and if correct, is rather an indication for
further precautions being taken to prevent access of pollution to deep
wells, than in favour of the continued use of river-water.
2. =Impurities of Transit from Source to Reservoir=, acquired during
the flow in rivers, canals, or other conduits. These impurities have
been broadly divided by the Rivers Pollution Commissioners into
“=sewage=” and “=manufacturing=;” the former including the solid and
liquid excreta, the house and waste water, etc.; the latter including
the refuse from manufacturing processes, as from dye and bleaching
works, tanneries, etc.
3. =Impurities of Storage=, whether in wells, reservoirs, or cisterns.
Organic impurities are commonly received at this stage. A well, for
instance, drains the soil around it in the shape of an inverted cone,
with a very broad base, unless the entrance of water from its sides is
prevented.
4. =Impurities of Distribution.= Lead, and occasionally other metals,
are dissolved by certain waters. If the pipes are left empty, as with
an intermittent supply, sewage may be drawn into them; in a few cases
coal-gas has found its way into the water pipes (page 76).
=Effects of Impure Water.=—1. =Effects of Mineral Impurities.=
_Suspended Mineral matters_ in unfiltered water occasionally produce
diarrhœa. The hill diarrhœa of some parts of India has been traced to
water containing fine mica particles in suspension.
=Hard water= is said by some to be hurtful, but the salts causing
hardness are probably innocuous when not amounting to more than 12 or
16 grains per gallon. Persons in the habit of drinking hard water find
soft water unpalatable. Hard water has been thought to favour gout and
calculus (stone), but this is not so. The salts producing permanent
hardness are said to be injurious, producing indigestion, but this is
doubtful in the amounts ordinarily drunk.
=Goitre=, a swelling of the thyroid gland in the neck, is often
associated with the use of drinking water from magnesian limestone
formations; but that any kind of excessively hard water causes goitre
is very doubtful.
=Lead= dissolved in water may produce serious and lasting ailments, and
they are often present for a long time before their cause is detected.
The amount of lead capable of producing poisonous symptoms has been as
little as 1∕100 grain per gallon of water (Dr. Angus Smith). According
to De Chaumont, 1∕10 grain per gallon, that is 1 part in 700,000 is
usually required to produce such symptoms. In the well-known case of
the poisoning of Louis Phillippe’s family at Claremount, there was
7∕10 grain of lead in a gallon of water; and this affected 34 per
cent. of those who drank it. The symptoms produced by lead poisoning
are those of indigestion, accompanied by colic; a blue line at the
junction of the gums with the teeth; “wrist drop,” a paralysis of the
muscles of the forearm, or some other paralysis; and if the poisoning
is continued, attacks of gout, followed by its usual consequences,
chronic kidney disease. The latter affections chiefly occur when the
poisoning is continued for a long time, as in the case of painters or
type-setters: poisoning from water is generally discovered before any
other than dyspeptic symptoms and colic are produced.
The presence of traces of iron in water may give it a slightly
astringent taste; and such water is liable to cause headache and
constipation.
2. =Effects of Vegetable Impurities.=—Living plants are
unobjectionable, but decomposing vegetable matter may produce diarrhœa
and other severe symptoms.
3. =Effects of Animal Impurities.=—Animal impurities of water are by
far the most important from a sanitary point of view. They are most
commonly derived from leaky drains or cesspools, or from surface
accumulations of filth. The quality of the contamination is more
important than its quantity; and this will explain why water containing
a large amount of sewage may be drunk for a prolonged period with
impunity, while at another time the least trace, if it contain the
active germs of disease, will lead to serious mischief.
Suspended animal impurities are much more dangerous than those
completely dissolved. Hence the examination of the colour and
turbidity of drinking water is very important. Fæcal contamination is
by far the most dangerous of all, and chiefly so when it is derived
from a patient suffering from some communicable disease, like enteric
fever or cholera.
=Certain Parasites= occasionally are swallowed with water in the form
of embryo or egg. The liver fluke, round worm, and less frequently
other kinds of entozoa have been introduced in this way. The occasional
swallowing of small leeches has occasionally given rise to hæmorrhage.
=Diarrhœa= may be caused by animal contamination of water. It most
often occurs in summer, when all the circumstances are favourable to
active fermentative changes. The summer diarrhœa of infants is caused
by similar changes in milk or other foods. The presence of fœtid gases
in water may lead to diarrhœa. This may occur when the overflow pipe of
a cistern opens into the soil pipe or into the trap of the W.C.
=Dysentery=, like cholera and enteric fever, may be propagated by water
contaminated with the stools of a patient suffering from the same
disease.
=Malaria or Ague= has been stated to be caused by the water of
malarious marshes. The evidence on this point requires revision,
in view of the part which the mosquito is now known to play in the
propagation of this disease (pages 282 and 307).
=Enteric= (_otherwise called Typhoid_) =fever= is most often due to the
drinking of water contaminated with sewage.
The balance of evidence is in favour of the view that in order to
produce enteric fever water must be contaminated with the stools
or urine of a patient who has suffered from this disease. Numerous
instances are on record in which villages, the inhabitants of which
drink sewage-contaminated water, have remained free from enteric
fever, until a patient suffering from it has come to the village,
when the spread by water has been very rapid. Occasionally no known
contamination from a case of enteric fever has preceded the outbreak
of this disease which has been caused by sewage-contaminated water. It
must be remembered on this point that the urine of an enteric fever
patient may occasionally contain large numbers of the bacillus causing
this disease for several months after the patient is well (page 301).
The contamination of water with sewage may occur in various ways. In
country places surface wells and small streams commonly supply the
drinking water, and these are frequently contaminated. The illustration
(Fig. 9) shows the percolation of excretory matters from an out-door
closet through the porous gravel, into a neighbouring well; the result
being an epidemic of enteric fever among those who drank the water of
the well. Alterations in the level of the subsoil water are sometimes
followed by an outbreak of enteric fever (p. 70). A sudden fall of rain
occurs, and the excess of water in the soil absorbs the soakings from
country privies or cesspools, and carries them into the nearest well.
The percolation of tainted water through a considerable tract of land,
possibly along fissures, is sometimes insufficient to purify it, as
proved by a remarkable epidemic in the small village of Lausen, in
Switzerland.
In other cases sewage gains access into leaky water-pipes. Formerly
contamination was occasionally due to improper connection between the
overflow pipe of the cistern and the soil-pipe, or to the water-closet
being flushed by a pipe directly connected with a water-main (as
in the Caius College outbreak at Cambridge), or connected with the
drinking-water cistern (page 76).
Milk may, by the admixture of water, become contaminated with enteric
matter, and produce widespread epidemics. Where the water is very
impure, the small amount used in washing cans may suffice to cause
infection.
_Cholera_ was first proved by Dr. Snow, in 1849, to be due to the
specific contagium of cholera gaining an entrance into drinking water.
This contagium is derived as in enteric fever from the intestinal
evacuations, the urine, and the vomit of patients suffering from the
same disease.
[Illustration: FIG. 9.]
The close connection of the spread of cholera with an impure water
supply has been repeatedly shown in this country. The cholera epidemic
of 1854 was very severe in the southern districts of London. At that
period these districts were supplied with water by the Southwark and
Vauxhall Company, deriving its water from the Thames at Battersea,
and by the Lambeth Company, having its intake at Thames Ditton, where
the water was purer. The two companies were acting in rivalry, so
that in many streets their mains ran side by side; and houses in the
same street similar in all other respects, received a different water
supply. An investigation of the distribution of cholera in these
districts gave the following results:—
POPULATION CHOLERA CHOLERA DEATHS
IN 1851. DEATHS IN PER 10,000
14 WEEKS. OF POPULATION.
Houses supplied by Southwark Co. 266,516 4,093 153
„ „ Lambeth Co. 173,748 461 26
The facts, when examined in detail, brought out still more strikingly
the exemption of the houses supplied by the Lambeth Company; the
infection picking out in a given street the houses supplied by the
Southwark Company. The great epidemic of cholera at Hamburg in 1892
proves the same point. Hamburg, Wandsbeck and Altona are three towns
adjoining each other, and really forming one large community; but while
Hamburg suffered terribly, the two other towns had no cases of cholera,
except the few that were brought into them. In all respects except
water-supply the conditions were alike; but Wandsbeck obtained filtered
water from a lake, Altona obtained filtered water from the Elbe below
the town, while Hamburg was supplied, previous to the epidemic, by
unfiltered water from the Elbe just above the town.
=Diphtheria= and scarlet fever have never been traced to polluted water.
=Effects of an Insufficient Supply of Water.=—The influence on personal
health is most baneful. Water is used sparingly for purposes of
cleanliness, with the necessary results that cutaneous diseases become
more common, and the whole body suffers; the linen is imperfectly and
infrequently washed; the house becomes dirty; drains are imperfectly
flushed; the streets are not cleaned; and the whole atmosphere becomes
loaded with impurities. According to Parkes, it is probable that the
almost complete disappearance of typhus fever from civilized and
cleanly nations, is not merely owing to better ventilation, but also to
more frequent and thorough washing of clothes.
Insufficient cleansing of the surfaces of streets and of sewers, owing
to a deficient supply of water, has a very important influence on
the spread of enteric fever and epidemic diarrhœa. A heavy fall of
rain often causes a rapid diminution in the prevalence of the latter
disease.