Physical Characteristics of Water:

Physical characteristics mainly include color, taste and odour, turbidity, temperature and conductivity.

Color

Pure water is colorless. Color in untreated water is mainly caused by following:

(a) Humic and peaty material.

(b) Naturally occurring metallic salts, mainly of iron and manganese.

(c) Algae.

(d) Discharge of untreated or partially treated water from industries. Water often appears colored (apparent color) due to material in suspension, while true color is contributed by dissolved solids which remain after removal of suspensions by pretreatment and filtration methods.

The color of water is usually expressed in Hazen units which are the same as the platinum-cobalt scale. The standard unit of color is that which is produced by one milligram of platinum cobalt dissolved in one litre of distilled water. Different standard color intensities representing 1 ppm, 2 ppm, 3 ppm etc. can be prepared by dissolving 1 mg, 2 mg, 3mg respectively of platinum cobalt in 1 litre of water. The color of a sample is inspected by comparing the color of the water sample with other glass tubes (called Neosler tubes) containing standard solution of different color intensities.

Small color intensities are measured by tintometer. The instrument is lighted from inside and contains an eye piece with two holes. A slide of standard colored water is seen through one hole and the slide of water to be tested is seen from the other hole. The colored slide is replaced by another till a match is obtained. The standard color intensity corresponding to the matching represents the intensity of color of the water sample being tested.

Although the maximum permissible color limit for public water supply is 20 on cobalt scale it should preferable be less than 10.