PHYSICAL CHARACTERISTICS OF WATER

The following are the physical characteristics

1.Turbidity

2.Colour and temperature

3.Taste and odour

TURBIDITY

Turbidity is caused due to presence of suspended and colloidal matter in the water. The character and amount of turbidity depends upon the type of soil over which the water has moved ground waters are less turbed than the surface water.

Turbidity is a measure of resistance of water to the passage of light through it. Turbidity is expressed as NTU (Nephelometric Turbidity Units) or PPM (parts per million) or Milligrams per litre (mg/l). Turbidity is measured by

1)Turbidity rod or Tape 

2) Jacksons Turbidimeter 

3) Bali’s Turbidimeter

The Sample to be tested is poured into a test tube and placed in the meter and units of turbidity is read directly on the scale by a needle or by digital display.

Drinking water should not have turbidity more than 10 N.T.U. This test is useful in determining the detension time in settling for raw water and to dosage of coagulants required to remove turbidity

COLOUR AND TEMPERATURE

Colour in water is usually due to organic matter in colloidal condition but some times it is also due to mineral and dissolved organic impurities. The colour produced by one milligram of platinum in a litre of water has been fixed as the unit of colour. The permissible colour for domestic water is 20ppm on platinum cobalt scale. The colour in water is not harmful but objectionable.

Temperature of water is measured by means of ordinary thermometers. The temperature of surface water is generally at atmospheric temperature, while that of ground water may be more or less than atmospheric temperature. The most desirable temperature for public supply between 4.4'C to 10'C. The temperature above 35'C are unfit for public supply, because it is not palatable.

TASTE AND ODOUR

Taste and odour in water may be due to presence of dead or live micro-organisms, dissolved gases such as hydrogen sulphide, methane, carbon dioxide or oxygen combined with organic matter, mineral substances such as sodium chloride, iron compounds and carbonates and sulphates of other substances. The tests of these are done by sense of smell and taste because these are present in such small proportions that it is difficult to detect them by chemical analysis. The water having bad smell and odour is objectionable and should not be supplied to the public.

The intensities of the odours are measured in terms of threshold number. This number is numerically equal to the amount of sample of water in C.C’s required to be added to one litre of fresh odourless water.