Addition of certain substances to the water such as organic, inorganic,
biological, radiological, heat, which degrades the quality of water so that it
becomes unfit for use.
Putrescibility is the process of decomposition of organic matter present in water by microorganisms using oxygen.
Water having DO (dissolved oxygen) content below 8.0 mg/L may be
considered as contaminated. Water having DO content below. 4.0 mg/L is
considered to be highly polluted.
Water pollution by organic wastes is measured in terms of Biochemical Oxygen Demand-(BOD). BOD is the amount of dissolved oxygen needed by bacteria in decomposing the organic wastes present in water.
Chemical oxygen demand (COD) is a slightly better mode used to measure pollution load in water. It is the measure of oxygen equivalent of the requirement of oxidation of total organic matter (i.e. biodegradable and non- biodegradable) present in water.
A cripling deformity called Minamata disease due to consumption of fish captured from mercury contaminated Minamata Bay.
Water contaminated with cadmium can cause itai itai disease also called ouch-ouch disease (a painful disease of bones and joints) and cancer of lungs and liver.
The compounds of lead cause anaemia, headache, loss of muscle power and bluish line around the gum
Excess nitrate in drinking water reacts with hemoglobin to form non -functional met haemoglobin, and impairs oxygen transport. This condition is called methaemoglobinemia or blue baby syndrome.
Over exploitation of ground water may lead to leaching of arsenic from soil and rock sources and contaminate ground water. Chronic exposure to arsenic causes black foot disease. It also causes diarrhoea,-peripheral neuritis, hyperkerotosis and also lung and skin cancer.