Past contamination of water is indicated by -
WATER POLLUTION Pure uncontaminated water does not occur in nature. It contains impurities of various kinds - natural and man- made. The natural impurities are not essentially dangerous. These comprise dissolved gases (e.g. nitrogen, carbon dioxide, hydrogen sulphide, etc. which may be picked up during rainfall), and dissolved minerals (e.g., salts of calcium, magnesium, sodium, etc.) which are natural constituents of wa'ter following its contact with soil; and suspended impurities (e.g., clay, silt, sand and mud), and microscopic organisms. These impurities are derived from the atmosphere, catchment area and the soil. * A more serious aspect of water pollution is that caused by human activity - urbanization and industrialization. The sources of pollution resulting from these are : (a) sewage, which contains decomposable organic matter and pathogenic agents (b) industrial and trade wastes, which contain toxic agents ranging from metal salts to complex synthetic organic chemicals (c) agricultural pollutants, which comprise feilizers and pesticides, and (d) physical pollutants, viz heat (thermal pollution) and radioactive Substances. The indicators of pollution include the amount of total suspended solids, biochemical oxygen demand (BOD) at 20 deg. C, concentration of chlorides, nitrates and phosphorus and absence of dissolved oxygen. Even if the source of water supply and its treatment are of a high standard, water pollution may still occur as often happens, due to corrosion of pipe lines, leaky joints and cross connections between water supply pipes and sewage drainage pipes. Surveillance has to be exercised at every point in the distribution system to ensure supply of safe water to the consumer. Ref: Park 25th edition Pgno : 760
Free and saline ammonia
Dissolved H2S
Nitrites
Nitrates
Environment and health