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22
Savage, an authority on the examination of water supplies,
says:—
"A working standard—that the finding of excretal Bacillus
Coli in 10 c.c. or less points to undesirable pollution—is both
justifiable and in accordance with actual experience. With
Bacillus Coli present in smaller amounts—e.g. 1 c.c. or less—the
water can be safely condemned as unsuitable for drinlsing purposes.
If no B. coli are present in 50 c.c. the water may probably be
safely passed as satisfactory as far as conditions actually present
are concerned."
In "The Examination of Water Supplies" by Drs. Thresh and
Beale, it is stated:—
"Where a public supply usually conforms to the high standard
given, even if Bacillus Coli is found in 100 c.c. and is absent in
50 c.c., it may be considered as satisfactory; if found in a much
smaller quantity—say in 10 c.c.—then further investigation is
necessary.''
The Analyses of the Richmond Water before treatment have
never shown Bacillus Coli in 10 ex., nor even in 50 c.c.
Treatment.
Practically all waters, no matter from what source they are
obtained, are liable to contamination and require some form of
treatment. This may be (1) Storage, (2) Filtration, (3) Chlorination.
Any two of these methods may be combined or all three methods
used together.
(1) Storage means the collecting of quantities of the water in
large open reservoirs. The water is allowed to remain there for a
considerable time permitting disease producing bacteria to die out.