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Water Quality Requirement for Different Uses

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For any water body to function adequately in satisfying the desired use, it must have corresponding degree of purity. Drinking water should be of highest purity. As the magnitude of demand for water is fast approaching the available supply, the concept of management of the quality of water is becoming as important as its quantity.

 

Each water use has specific quality need. Therefore, to set the standard for the desire quality of a water body, it is essential to identify the uses of water in that water body. In India, the Central Pollution Control Board (CPCB) has developed a concept of designated best use. According to this, out of the several uses of water of a particular body, the use which demands highest quality is termed its designated best use. Five designated best uses have been identified. This classification helps the water quality managers and planners to set water quality targets and design suitable restoration programs for various water bodies.

 

Designated Best Uses of Water

Designated Best Use

Class

Criteria

Drinking Water Source without conventional treatment but after disinfection

A

1.Total Coliforms Organism MPN/100ml 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 20 C, 2mg/l or less

Outdoor bathing (Organised)

B

1.Total Coliforms Organism MPN/100ml 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 20 C, 3mg/l or less

Drinking water source after conventional treatment and disinfection

C

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

2. pH between 6 and 9

3. Dissolved Oxygen 4mg/l or more

4. Biochemical Oxygen Demand 5 days 20 C, 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)

4. Biochemical Oxygen Demand 5 days 20 C, 2mg/l or less

Irrigation, Industrial Cooling, Controlled Waste disposal

E

1. pH between 6.0 and 8.5

2. Electrical Conductivity at 25 C micro mhos/cm, maximum 2250

3. Sodium absorption Ratio Max. 26

4. Boron Max. 2mg/l

 

Below-E

Not meeting any of the A, B, C, D & E criteria

Source: CPCB

 

            A colour coding frequently used to depict the quality of water on maps

Blue water 

This water can be directly used for drinking, industrial use, etc.

Green water 

Water contained in soil and plants is termed as green water

White water  Atmospheric moisture is white water
Brown or grey water   Various grades of wastewater are shown by brown or grey colour

                   

In India, CPCB has identified water quality requirements in terms of a few chemical characteristics, known as primary water quality criteria. Further, Bureau of Indian Standards has also recommended water quality parameters for different uses in the standard IS 2296:1992.

 

Water Quality Standards in India (Source IS 2296:1992)

Characteristics

Designated best use

A

B

C

D

E

Dissolved Oxygen (DO)mg/l, min

6

5

4

4

-

Biochemical Oxygen demand (BOD)mg/l, max

2

3

3

-

-

Total coliform organisms MPN/100ml, max

50

500

5,000

-

-

pH value

6.5-8.5

6.5-8.5

6.0-9.0

6.5-8.5

6.0-8.5

Colour, Hazen units, max.

10

300

300

-

-

Odour

Un-objectionable

 

-

-

Taste

Tasteless

-

-

-

-

Total dissolved solids, mg/l, max.

500

-

1,500

-

2,100

Total hardness (as CaCO3), mg/l, max.

200

-

-

-

-

Calcium hardness (as CaCO3), mg/l, max.

200

-

-

-

-

Magnesium hardness (as CaCO3), mg/l, max.

200

-

-

-

-

Copper (as Cu), mg/l, max.

1.5

-

1.5

-

-

Iron (as Fe), mg/l, max.

0.3

-

0.5

-

-

Manganese (as Mn), mg/l, max.

0.5

-

-

-

-

Cholorides (as Cu), mg/l, max.

250

-

600

-

600

Sulphates (as SO4), mg/l, max.

400

-

400

-

1,000

Nitrates (as NO3), mg/l, max.

20

-

50

-

-

Fluorides (as F), mg/l, max.

1.5

1.5

1.5

-

-

Phenolic compounds (as C2H5OH), mg/l, max.

0.002

0.005

0.005

-

-

Mercury (as Hg), mg/l, max.

0.001

-

-

-

-

Cadmium (as Cd), mg/l, max.

0.01

-

0.01

-

-

Salenium (as Se), mg/l, max.

0.01

-

0.05

-

-

Arsenic (as As), mg/l, max.

0.05

0.2

0.2

-

-

Cyanide (as Pb), mg/l, max.

0.05

0.05

0.05

-

-

Lead (as Pb), mg/l, max.

0.1

-

0.1

-

-

Zinc (as Zn), mg/l, max.

15

-

15

-

-

Chromium (as Cr6+), mg/l, max.

0.05

-

0.05

-

-

Anionic detergents (as MBAS), mg/l, max.

0.2

1

1

-

-

Barium (as Ba), mg/l, max.

1

-

-

-

-

Free Ammonia (as N), mg/l, max

-

-

-

1.2

-

Electrical conductivity, micromhos/cm, max

-

-

-

-

2,250

Sodium absorption ratio, max

-

-

-

-

26

Boron, mg/l, max

-

-

-

-

2

 

 Guidelines are available to evaluate quality of water for irrigation. For irrigation, water can be classified in five classes depending upon its chemical properties.

Guidelines for Evaluation of Irrigation Water Quality

Water class

Sodium (Na) %

Electrical conductivity (mS/cm)

SAR

RSC meq/l

Excellent

< 20

< 250

< 10

< 1.25

Good

20 - 40

250 750

10 18

1.25 2.0

Medium

40 - 60

750 2,250

18 26

2.0 2.5

Bad

60 80

2,250 4,000

> 26

2.5 3.0

Very bad

> 80

> 4,000

> 26

> 3.0

 

Drinking Water Specifications (IS 10,500:1991)

Characteristics

Desirable limit

Permissible limit

Essential Characteristics

Colour, Hazen Units, Max

5

25

Odour

Unobjectionable

-

Taste

Agreeable

-

 Turbidity, NTU, Max

5

10

PH value

6.5 to 8.5

-

Total Hardness (as CaCo3), mg/l, Max

300

600

Iron (as Fe), mg/l, Max

0.3

1.0

Chlorides (as Cl), mg/l, Max

250

1,000

Residual free chlorine, mg/l, Max

0.2

-

Desirable Characteristics

Dissolved solids, mg/l, Max

500

2,000

Calcium as (Ca), mg/l, Max

75

200

Magnesium (as Mg), mg/l, Max

30

75

Copper (as Cu), mg/l, Max

0.05

1.5

Manganese (as Mn), mg/l, Max

0.1

0.3

Sulphate (as So4), mg/l, Max

200

400

Nitrate (as No3), mg/l, Max

45

100

Flouride (as F0, mg/l, Max

1.0

1.5

Phenolic compounds (as C6H5OH), mg/l, Max

0.001

0.002

Mercury (as Hg), mg/l, Max

0.001

-

Cadmium (as Cd), mg/l, Max

0.01

-

Selenium (as Se), mg/l, Max

0.01

-

Arsenic (as As), mg/l, Max

0.05

-

Cyanide (as CN), mg/l, Max

0.05

 

Lead (as Pb), mg/l, Max

0.05

-

Anionic detergents (as MBAS), mg/l, Max

0.02

1.0

Chromium (as Cr6+), mg/l, Max

0.05

-

PAH, mg/l, Max

-

-

Mineral oil, mg/l, Max

0.01

0.03

Pesticides, mg/l, MAX

Absent

0.001

Alkalinity, mg/l, Max

200

600

Aluminum (as Al), mg/l, Max

0.03

0.2

Boron, mg/l, Max

1

5