Z 
large and well-constructed tanks, for in many districts large 
lakes have been built in order to store water both for drinking 
and irrigation purposes. Of course ground water, obtained 
from wells, is used where local conditions are favourable, but 
a large proportion of the inhabitants prefer lake or river water, 
if it is obtainable. 
When one considers the rivers of the East, we appear to 
be dealing with a subject that has no parallel in the West, 
so great is the difference between the sewage-polluted streams 
of England and the mighty floods, such as the Ganges, the 
Indus, the Irrawaddy, the Mahanuddi, the Kistna, the Brah- 
maputra, and a hundred others that occur to one. All of 
these are many hundreds of miles in length; they move slowly 
over a flat country; at certain times of the year they broaden 
out into wide expanses of shallow clear water resting on a bed 
of clean sand. It isimpossible to give any idea as to how long 
it would take for any particular drop of water to pass from 
the source of one of these leviathans to the sea. Towns of 
course exist on their banks, but comparatively few of these 
have an underground drainage system, or pipe water-supply, 
so that although the pollution may be very deadly in charac- 
ter, the quantity is so small that it is but as a drop in the 
ocean. The contamination occasioned by a large town, such 
as Benares, is relatively so small that it is not always easy to © 
trace it a few miles down the river. Of course, along both 
banks, there is a constant trickle of contamination greater 
or smaller in amount in different places. Yet, in spite of the 
small amount of polluting material, we have to explain the 
fact that evidence of fecal contamination can nearly always 
be found even in small quantities of water. 
To turn to the climatic conditions, for 7 or 8 months of 
the year most of these rivers flow under an almost cloudless 
sky. The sun’s rays are practically vertical, the. amount 
of evaporation from the surface is great, the water is in 
many cases clear. So great may be the combined result of 
these natural forces that it is occasionally possible to obtain 
a sample from the middle of the Ganges in May, which will 
contain no glucose fermenting faecal organism in 100 cubic 
centimetres. 
