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CHAPTER XIV.
CHEMICAL ANALYSES OF WATER SUPPLIES IN THE, MADRAS PRESIDENCY.
During two quarters of the year under report chemical analyses of the various
samples have been carried. out. Table No. XIV( a) gives the results obtained. in a way
which renders it possible to survey the results as a whole. We do not propose to
enter into a long discussion of each of these several samples but just to indicate a few
of the main differences which appear to exist between the waters in Europe and those
of India.
As a whole the waters cannot be called very satisfactory as judged. by English
standards. The actual quantity of fœcal contamination is apparently great, but, on the
other hand, certain conditions exist in India which render the judging of waters, by
standards applicable to England, a somewhat doubtful proceeding. This point will
be referred to later on. Chemically speaking, the best waters are the upland. surface
waters in the hill stations of Coonoor and Ootacamund. The total solids are very low,
the water is very soft, and the ammonia, free and albuminoid, is not excessively high
for this country. A comparison should be made between the water supplies of Madras
a nd Oot a c a mund; t h e f o r me r b e i n g d e r i v e d f r o m a . s u r f a c e wa t e r o n t h e p l a i n s . Th e
hi gh t ot al sol i ds and hardness, compared wi t h t he Oot acamund resul t , wi l l be observed.
Also the larger quantity of the ammonias present. The Madras supply may be taken
as a typical plains surface water derived from a large catchment area, where no
attempt is made to either avoid or lessen the amount of pollution. On the hillsides
in Ootacamund care is taken to prevent pollution and the catchment areas are
carefully conserved.
The raw river waters show very great variation in the quantities of their saline
constituents, but all these have a tendency to be high. The ammonias also are for the
most part excessive.
The well and spring waters are almost invariably hard and contain large quantities
of nitrates.
The real interest, however. of these tables lies in a study of the ammonia figures,
taken in conjunction with the nitrates present. First of all we wish to call particular
attention to the extraordinary rarity of nitrates in all the surface waters (with one
exception *) and. the large quantities of these in all sub-soil waters. In nearly all
the analyses of surface waters the nitrates are recorded as either nil or a trace. Further
the ammonia figures, both albuminoid and free, are, relatively speaking, higher than
is usual in drinking waters in England. These facts demonstrate that the amount of
nitrification which goes on, on the surface of the ground, in the Madras Presidency, is
extremely small. It is well known to all who have had any experience of sewerage
works in Europe that a shower of rain in a town is usually followed by the presence of
nitrates in the sewage due, in all probability, to the washing in of nitrates from the
surface of the ground. Apparently this condition does not exist in India, otherwise
the rarity of nitrates in the surface water would not be so marked. On the other
hand, it will be observed that in ground waters, nitrification has gone on in the usual
manner, for all such supplies are rich in the salt ; the free, and particularly the
albuminoid, ammonia being proportionately reduced. The explanation of this want of
power of the surface layers of the ground to nitrify ammonias, is probably to be found
in the fact that nitrifying organisms on the surface do not survive the heat and
dessicating action of the tropical sun. Boulanger and Massol have shown, that certain
varieties isolated by them, are very susceptible to high temperatures. This may be the.
explanation of the want of nitrifying powers of the surface layers of soils in India. The
obvious conclusions from these remarks, is that the standards usually accepted in England
*The sample from Gudiyattam. which contains large quantities of nitrates, is taken from an infiltration gallery
in the sandy bed of the Palar, the bed is badly fouled not far above the gallery, which may explain the presence of
the nitrate, or it may be due to a salt strata in the sand, as both chlorides and hardness figures are high.