in time a dense mat of vegetation on the surface, the water, it is said, becomes unfit to drink, and gives out deleterious gases.
But, in point of fact, such cases are extremely rare. As a rule the surface of every tank or collection of water falls several feet during the dry months, and exposes a margin of damp soil more or less saturated with organic matter, which is, of course, unhealthy.
Lower Bengal is one mass of tanks, mostly very small, in which every kind of pollution collects all through the dry season; and from these in many places the people drink. All are natural hollows or formed by excavation—not, as in South and Central India, by damming up the outlets of valleys and hollows. But very few are dug out to such a depth as to leave, during the hot months, a sufficient depth of water to prevent decomposition, and fewer still are properly cleansed and protected from defilement by organic impurities.
Even in Bengal it is the poverty, not the will, of the people that consents to drink bad water. Whenever they have the means, they are glad to fence and line their tanks and wells with masonry. A sure sign of a thriving landowner is: masonry tanks and wells on his property. The rich often bring their water from immense distances, in sealed jars, on men's heads; and there is no such popular application of taxation as in improved water-supply.
Sub-soil water level.2. Observations of the level of sub-soil water are doubtless most important.[1] It is stated, however,- ↑ The precise relation between the level of the subsoil-water and
