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The Commission obviously does not consider it necessary that these natural processes should
in themselves be sufficient to render a water supply fit for domestic purposes, but is satisfied if such
agencies and the operations of the water companies combined, suffice to insure that wholesome water
is supplied to the consumers. As evidence that this is the view of the Commission, I may cite
the following statement in their report, which follows a reference to the well-known cases
of the distribution of cholera in 1854 by water from a well in Broad-street, Golden-square, and of
enteric fever in 1879 by water from a well in Caterham. " The question, however, is not whether such
dissemination is possible under any circumstances, but whether water, however slightly contaminated,
can be freed from such contamination by proper precautions, such as adequate storage and filtration, or
whether, as contended, it must be regarded as for ever unsuitable for drinking purposes."
Now it is probable that the completeness of the future operations of the water companies may
depend upon the necessity which can be shown for efficient filtration, using the word efficient in the
sense which is indicated by recent observations. It is therefore a matter of great importance that the
natural processes of purification should not be held to be more deserving of reliance than they actually
are. I have therefore studied the statements in the Commission's report which bear upon this
subject, with the result that I am led to think that some of the reasons given for assuming that the
London population is not exposed to risk, are less deserving of acceptance than appears at first sight.
Dilution of polluting matter.
The Royal Commission has evidently been impressed by the dilution to which any excremental
matter must be subjected which enters its waters. Thus the Commission, after taking the smallest
annual flow in the Thames over Teddington weir in any one of the eleven years 1881-91, and the largest
estimated number of cases of enteric fever in any one of those years (1,001), shows that this would
give 294 million gallons to one case, " an amount which perhaps may be more readily apprehended if
described as a mass five miles in length, one hundred yards in width and six feet in depth. A similar
calculation made for the Lea gives for each typhoid case a body of water three miles in length, one
hundred yards in width, and six feet in depth."
I confess that this argument appears to me to be open to objection. The risks to London water
supplies are less from the average number of cases of enteric fever in the water area in a year than
from the occurrence of a number of cases at any one time in a community which discharges its sewage
into the rivers. Thus, typhoid fever is not usually distributed equally throughout the year, but is
especially prevalent in certain mouths, and if this circumstance only were considered, the volumes of
Thames and Lea water given in the above paragraph would for these periods have to be differently stated.
In estimating risk of this kind, regard must be had for the possibility of some exceptional outbreak,
due perhaps to milk, and giving rise to hundreds of cases of this malady in the towns situated
a limited number of miles above the intakes, and discharging their sewage into the rivers. No doubt
the treatment of this sewage before its discharge is, under ordinary circumstances, a safeguard of much
value, but there has been experience of a town having to discharge its sewage untreated into a river,
owing to a temporary failure in its machinery for treatment, and this at a time when the town was
suffering from an epidemic of enteric fever. For the safety of Londoners, the natural processes of
purification and the operations of the water companies must uninterruptedly be equal to the demand
which would be made upon them in such an event.
Again, referring to the outbreak of enteric fever in Caterham in 1879, the Commission states—
" It appears from returns made by the Chairman of the Caterham Water Company that the total
amount of water pumped from the well in the 14 days, during which it was being continually
polluted, was 1,861,000 gallons. But if the volume of water brought down by the Thames to the
intake be taken into account, and also the fact that at least 98 per cent. ef tho microbes in water are
removed by filtration, it will be found on calculation that in order to produce an equal amount of
pollution in the water supplied to the London consumers to that of the Caterham well, nearly half-amillion
cases of typhoid fever must occur in a fortnight in the Thames valley above the intake, the
discharges from all these cases passing into the river as directly and in as great a proportion as did the
discharges of the workmen into the Caterham well, and no part of these discharges being arrested or
destroyed on their way down to the Hampton intakes or during the sojourn in the subsidence tanks.
But the entire population of the valley above Hampton consists—men, women, and children—of only
about one million persons."
In estimating the value of this argument in connection with London water supply the following
circumstances must be remembered. There is no accurate knowledge of the amount of water which a
single case of enteric fever can render virulent, and certainly no safe deduction of this kind can be made
from the occurrence at Caterham. The man who infected the water in the Caterham well suffered from a
comparatively mild attack of enteric fever, i.e., he was only confined to his bed for two days, and it is quite
likely that the evacuations of mild cases of the disease are less virulent than those of severe cases. He
was only employed in this well during certain hours of work, and it may therefore be assumed that but
a portion of his daily excreta were evacuated during these working hours. At other times he had no
opportunity of polluting the water. It must also be remembered that he insisted that when in the well
he used the bucket, and that his evacuations were sent to the surface. It may therefore be that the
contamination of the water, which was pumped was effected by mere splashings from the bucket. But
whatever quantity of his excreta entered the well, it is impossible to assume that it rendered virulent as
much water as it was capable of rendering virulent, for the multiplication of the bacillus in water must
be accepted; all we know is that the water company pumped 1,861,000 gallons in a fortnight, and it is
quite possible that if the company had pumoed a much larger volume of water, this larger amount
would have been found to be infective.
For all we know, less than part of this man's daily excreta may have polluted the well
water; the excreta may have contained matter the virulence of which was only 1/10 of that of the