VPE 511: Environment and Environmental Hygiene (2+1)

FAUNA OF WATER SUPPLIES

• Members of all the chief groups of fresh water animals are to be found in one or other of the various sources from which water supplies are drawn.
• They may gain access to purification plants at waterworks, but rarely cause serious trouble in these.
• In the past, before the sand filtration of public water supplies was universally adopted , there are several instances where Sponges, Polyzoa and Mollusca are reported to have flourished abundantly in service pipes and mains.
• The sand filtration of water effectively excludes the minute larval stages of these animal types, which can pass readily through the strainers used to stop the grosser inclusions of natural waters.
• Should these larvae, on the other hand, gain access to the water pipes, they may lodge at suitable sites and develop into the adult forms. The latter feed on Diatoms and other Algae which are invariably present in unfiltered water, and may multiply so greatly as to seriously reduce the capacity of the pipes.
• They afford lodgment, too, to a whole host of organisms which would otherwise to swept on by the current, and when members of this pipe fauna die their decay pollutes the water and favors the growth of saprophytic bacteria.
• The common freshwater fishes are usually to be found in sources of water supply, such as rivers and natural lakes.
• They are thought to exercise a beneficial influence on the quality of the water, in that they feed on the smaller plant and protozoal forms, and so possible limit the numbers of these.
• For this reason, artificial impounding reservoirs for the storage of water are commonly stocked with fish, generally trout.