View report page

8
It is not now probable that those circumstances will ever be known, but Dr. Barry's report
contains certain statements deserving of attention in this connection. Referring to the Darlington
Corporation Waterworks, he says, "The rate of filtration is from 3 to 4 inches per hour, or about 45
gallons per 24 hours, per superficial foot of filter. The surface of each filter is stated to be cleansed
on an average once in six weeks, on each occasion about 1½ inches of the sand being scraped off from
the top and washed with water in a tub by agitation with rakes. The whole of the sand in such filter
is washed on an average once in three years."
Referring to the Stockton and Middlesbrough Water Works, Dr. Barry says, " The rate of
filtration is about 6 inches per hour, or about 63 gallons per 24 hours per superficial foot of filter."
Koch's standard would give approximately 49 gallons per superficial foot of filter per 24 hours,
and the rate of filtration of the former waterworks is therefore 4 gallons less, and that of the latter
14 gallons more than this standard.
The rates of filtration of the Tees waterworks may perhaps be averages, including periods of
greater and less rapid flow through the filters. Under any circumstances the flow through the filters
of the Stockton and Middlesbrough Water Board was such that it would, according to Koch, not be
regarded as efficient filtration. And again there may have been periods when thorough cleaning of
the filters, or when other circumstances already alluded to, interfered with the proper action of the filter
beds of both companies.
Definition of efficient filtration.
Section 4 of the Metropolis Water Act, 1852, requires every company to effectually filter all
water supplied by them within the metropolis for domestic use. Dr. Edward Frankland, in discussing
the meaning of the expression "efficient filtration," as understood in 1852, said in his further
statement " at that time, the definition of ' efficiently filtered' would doubtless be ' clear and transparent
to the eye,' that is to say, free from all obvious suspended matters. . . . The definition, however,
of efficient filtration, which was thought to be sufficiently stringent in 1852, when the bacteriological
effect of the process was entirely unknown, has now become obsolete and ought to be amended. We
now know that the possible noxious matters in river water are not the mineral or even organic, as
distinguished from ' organised ' materials, but living microbes, and that the only efficient filtration,
from a sanitary point of view, is that which removes the whole or nearly the whole of these microbes
from the water."
The Commission clearly states the need for the operations of the companies being in every way
complete, and includes in its report the following paragraph—
" The water that flows down to the intakes must be subjected to certain important processes,
before it is brought into a suitable condition for delivery and consumption."
" These processes consist of subsidence and filtration, and the quality of the water when delivered
depends largely on the thoroughness with which they are carried out. It does not come within the
terms of our reference to lay down what should be the exact regulations as regards filtration, that is to
say, what should be the proportionate area of the filtering beds, the depth of sand, the frequency of
renewal, or the rate at which the water should be allowed to percolate ; nor, as regards the subsidence
tanks, how many days storage should be deemed sufficient so as to obviate the necessity of taking in
turbid storm water, and to allow of due settlement; but we cannot shut our eyes to the fact that the
provision for these purposes differs enormously in the different companies, and in some of them is to
our mind quite inadequate."
" Regulations on these matters should be drawn up after competent inquiry, and adherence to
these regulations should be strictly enforced."
This question is not of concern to London only, but to all communities supplied from
running waters receiving pollutions, and the necessary corollary to the report of the Royal Commission
on Metropolitan Water Supply is the issue of another Royal Commission to make such enquiry and
such experimental investigation as may be required to determine the precise conditions to which
polluted streams must be subjected in order to make their water uninterruptedly fit for domestic use.
Conclusion.
In view of the changes effected in the rivers, and subsequently in the filters, the risk to
Londoners is, I believe, small and certainly intermittent, and indeed may be thought of as comparable
to those possibilities of injury from accident in the street to which every human being is subject
during the whole of his life. The risk, indeed, is to each a possibility, and not a probability, but such
as it is, I believe it exists.
If we recognise, as I believe we may, that the safety of London residents is dependent upon the
efficiency with which deleterious matter in the London rivers is by artificial means removed from the
water supplied to the metropolis, the conditions under which this removal is to be continuously
ensured must obviously be determined with absolute precision, and an administration must be provided
to secure that the object in view shall be attained.
Shirley F. Murphy,
Medical Officer of Health.
Public Health Department,
Spring Gardens, S.W.,
17th January, 1894.