Envis Centre, Ministry of Environment & Forest, Govt. of India

Printed Date: Wednesday, May 22, 2024

Quality

Water quality classification

 

Parameters to decide river quality


Water quality is measured in terms of parameters like biochemical oxygen demand (BOD), dissolved oxygen (DO) and total coliform count. BOD is a measure of water pollution based on the organic material it contains. The organic material provides food for aerobic bacteria, which require oxygen to be able to bring about the biodegradation of such pollutants. The greater the volume or organic material and the greater the numbers of bacteria, the greater will be the demand for oxygen. Thus, the BOD value gives an indication of organic pollution levels in the water. If BOD exceeds the available dissolved oxygen in the water, oxygen depletion occurs, and aquatic organisms suffer. Fish kills are not uncommon under such circumstances.

When organic effluent is added to a stream, the demand for oxygen from bacteria and other organisms which will digest the organic matter, and from chemical oxidation processes, is met by the oxygen dissolved in the water. Thus, immediately downstream from the effluent source, the DO content of the stream falls. As the organic material is gradually decomposed and converted into carbon dioxide (CO2 ) and water, the demand for oxygen declines. Ultimately, the availability of oxygen exceeds its use and dissolved oxygen levels in the stream rise again.

River water quality usage is classified as follows: Class A means drinking water source without conventional treatment, Class B allows water to be used for outdoor bathing, Class C for drinking water with conventional treatment, Class D is fit for wildlife and fisheries, and Class E means water is fit for recreation and aesthetics, irrigation or industrial cooling.

 

PRIMARY WATER QUALITY CRITERIA FOR DESIGNATED BEST - USE - CLASSES

Classification

Category

Tolerance Limit

Drinking Water Source without conventional treatment but after disinfections

A

1.     Total Coliform Organism MPN/100 ml shall be 50 or less

2.     pH between 6.5 and 8.5

3.     Dissolved Oxygen 6mg/l or more 

4.     Biochemical oxygen demand 5 days 20oC 2mg/l or less

Outdoor Bathing (Organized )

B

1.     Total Coliforms Organism MPN/100 ml shall be 500 or less

2.     pH between 6.5 and 8.5

3.     Dissolved Oxygen 5mg/l or more

4.     Biochemical Oxygen Demand 5 days 20oC 3mg/l or less

Drinking Water source after conventional treatment and disinfections

C

1.     Total Coliforms Organism MPN/100 ml shall be 5000 or less

2.     pH between 6.5 and  8.5

3.     Dissolved Oxygen 4mg/l or more

4.     Biochemical Oxygen Demand 5 days 20oC 3mg/l or less

Propagation of Wild Life and Fisheries 

D

1.     pH between 6.5 and 8.5

2.     Dissolved Oxygen 4mg/l or more

3.     Free Ammonia ( as N )1.2 mg/l or less

Irrigation  Industrial   Cooling,  Controlled waste disposal 

E

1.     pH between 6.0 and 8.5

2.     Electrical Conductivity at 25oC micro mhos/cm Max. 2250

3.     Sodium absorption ratio Max. 26

4.     Boron Max. 2 mg/l

 Source: UP Pollution Control Board.