Understanding Water Quality : A Quick Look Into The CPCB Norms

Water is probably the most important natural resource, second only to air! While water is available in sufficient quantities for all human requirements, non-uniform distribution of water in different parts of the world and even within a country makes wise use of water and understanding water quality not only a necessity but the very crucial factor for day-to-day life and activities.

With the rising concentrated use of water in geographies like metropolitan cities and industrial zones, it has become absolutely necessary that we keenly monitor the quality of water that we use for different activities. Central Pollution Control Board(CPCB) has laid detailed guidelines about water quality and what industry needs to do measure and maintain it.

Unclean Water And Emission Of Industrial Waste
Industrial Emission

1. How Is Water Quality Defined?

Before we actually look at water quality guidelines prescribed by CPCB (Central Pollution Control Board), it will be worthwhile to have a look at different parameters that define water quality.

Parameters are:

  • pH: pH is a logarithmically plotted figure which tells how acidic or alkaline any fluid is. pH value of 7 corresponds to a neutral fluid which is neither acidic nor alkaline. pH value believes 7 indicates acidic nature of the fluid while pH value above 7 indicates the alkaline nature of the fluid.
  • Dissolved Oxygen (DO): Water normally contains a certain amount of dissolved oxygen molecules which get dissolved in water via diffusion during the aeration process. Dissolved oxygen generally improves the taste of the water. Very high quantities of dissolved oxygen will lead to corrosion of pipelines and storage vessels. DO is measured in mg/liter of water.
  • Coliforms Organism: Coliforms organisms are a group of bacteria which are normally present in environment. The source of these bacteria is feces of humans and other warm-blooded animals. Presence of coliform bacteria indicates presence of harmful, disease causing and spreading bacteria in the water. They are measured in MPN/100 ml where MPN is Most Probable Number.
  • Biochemical (or Biological) Oxygen Demand (BOD): BOD refers to amount of dissolved oxygen required by aerobic biological organisms to break down organic material present in any given water sample. BOD is generally measured in mg per liter of oxygen consumed over 5 days at a temperature of 20 Degree Celsius.
  • Other parameters: Apart from the above mentioned parameters, some other water parameters need to be monitored depending on the application. These parameters include free ammonia, Boron, Sodium absorption ratio, Electrical conductivity etc.

water quality

2. What Are CPCB (Central Pollution Control Board) Standards For Water Quality Monitoring?

Now that we know the critical parameters for measuring water quality, let us have a look at how CPCB defines water fit for different activities.

CPCB categories water into 5 categories, namely A, B, C, D, and E.

The table below explains possible usage and quality guidelines for these types:

Type Usage Guidelines
A Drinking Water Source without conventional treatment but after disinfection  pH between 6.5 and 8.5


Dissolved oxygen 6mg/l or more.

BOD 2mg/l or less.

B Outdoor bathing (Organized)   Total Coliforms Organism MPN/100ml shall be      500 or less


pH between 6.5 and 8.5

Dissolved Oxygen 5mg/l or more

BOD 3mg/l or less.

C Drinking water source after conventional treatment and disinfection   Total Coliforms Organism MPN/100ml shall be       5000 or less


pH between 6 to 9

Dissolved Oxygen 4mg/l or more

BOD 3 mg/l or less.

D Propagation of Wildlife and Fisheries   pH between 6.5 to 8.5


DO 4mg/l or more.

Free Ammonia 1.2 mg/l or less

E Irrigation, Industrial Cooling, Controlled Waste disposal   pH between 6.0 to 8.5


Electrical Conductivity of Max 2250 micromhos/cm at 25 Degree C.

Sodium absorption ratio of Max 26.

Boron: maximum 2mg/l.

Water which does not meet above criteria is classified as below E.

From the above table, it is quite clear that how important it is to monitor the quality of the water at the inlet and also at the point of discharge in any industry. This makes installing a Water Quality Monitoring System a must; not only to avoid legal implications but also to safeguard and ensure the well being of the community that we operate in.