Water pollution is the loss of potency of water for beneficial uses due to addition of an excess of material that is harmful to humans, animals or aquatic life due to human activity.
Water is used in day to day life for various purposes beneficial to mankind and these include its use for drinking, for watering livestock and the irrigation of crops, for fisheries, for industry, for food production and for recreational and amenity use.
Normally water contains natural impurities like dissolved gases (H2S, C02, N2), dissolved minerals (Ca, Mg, Na salts), suspended matter (clay, silt, sand) and microbes. But these impurities are present in a very low amount.
Thus non-polluted water contains these impurities in such a low amount that it is potable. Any substance that disallows the normal use of water is called as water pollutant. Polluted waters are turbid, unpleasant, bad smelling, unfit for drinking and washing and other purposes.
Sources of water pollution
(A) On the basis of genesis
i) Natural sources (decomposed vegetables, animal and weathered products)
ii) Manmade sources (industrial, agricultural, urban, domestic, radioactive etc.)
(B) On the basis of discharge pattern
i) Point source (well defined locations e.g. sewage outlet from an industry or municipal discharge)
ii) Non-point source (spread over larger areas and dispersal in nature e.g. water runoff grazing land, construction sites, agricultural farms, mining areas etc.)
The water pollutants can be classified into three groups, according their physico-chemical properties.
i) Soluble pollutants
These pollutants are completely soluble in water. These impurities are invisible impurities and can thus only detect by chemical analysis.
These pollutants include easily soluble gases like N2 COH2S etc., soluble salts like Na, K, Ca, Mg, Al, Fe and Mn, salts of heavy metals such as Cu Pb, Mg, Cd, Hg, As, Zn, Ni etc. and various organic substances such as formaldehyde, phenols etc.
ii) Colloidal pollutants
These impurities form colloidal solution with water. These pollutants include Si02, Al(OH)3, Fe(OH)3 (minerals), humic acid and folic acid (organics) etc.
iii) Insoluble pollutants
These pollutants form suspensions in water. Such impurities include sand, clay and organic matter.
Water pollutants on the basis of their nature can be classified as
i) Inorganic pollutants (Heavy metals, chlorine, S02, H2S)
ii) Organic pollutants (formaldehyde, phenols, ketones, phenols)