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WATER SUPPLY.
The water supplied to the district by the West
Middlesex and Grand Junction Waterworks Companies
has maintained its excellence, that of the
former Company being on the whole the better.
Table 26 shows the amount of, and range of variation
in, the purification effected by the settlement and
filtration which the water undergoes before distribution,
and Table 27 compares the mean results of last
year with those of the three preceding years.
Valuable as are the results and information
obtained by the chemical analysis of a water of known
composition, especially when such analysis is made at
frequent intervals, it is necessary to supplement it by
biological examination and inspection of, and supervision
over, the area whence the water is derived.
The biological examination of water is as yet but
imperfectly understood, and usually consists in an
enumeration of the number of "colonies" which may
be developed from a minute standard quantity
of water. On special occasions a careful search will
be made for such micro-organisms as are known to be