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Water Quality Concerns

Minimum and Desirable constituents to be determined for common uses of water

Domestic Public supply Irrigation General Industrial Supply
Suggested minimum analysis Iron Hardness
Detergents
Fluorides
Silica Iron
Manganese
Magnesium
Bicarbonate
Sulphate Chloride,
Fluoride,
Nitrate,
Dissolved solids pH,
Colour,
Turbidity,
Phenols Detergents Heavy metals
Calcium
Magnesium
Sodium Bicarbonate
Boron Spec.Conductance
Iron,
Magnesium
Sodium Bicarbonate
Hardness Dis.solids
ph
Temperature
Desirable additional analysis Manganese Bicarbonate
Sulphate Chloride Nitrate Diss.solids,
pH
Lithium
Sulphate
Chloride
Diss.solids
Silica Chloride Colour,
Turbidity Sulphide

As per World Health Organisation (WHO) and Indian Standards, the permissible limit of various constitutents in the potable water is as follows:

Standards and Criteria for drinking water in mg/I

Substance of Property World Health Organisation Public Health Committee of Govt. of India
Maximum acceptance Maximum Allowable Permissive Excessive
Physical Manganese Bicarbonate
Sulphate Chloride Nitrate Diss.solids,
pH
Lithium
Sulphate
Chloride
Diss.solids
Silica Chloride Colour,
Turbidity Sulphide
Turbidity (Units) 5 25 5 25
Colour (Platinum Cobalt Scale) 5 50 5 25
Taste and Odour Unobjectionble - Unobjectionble -
Chemical
pH range 7- 8.5 - 7- 8.5 -
Total Solids 500 1500 500 1500
Total hardness as CaCo3 - - 300 600
Calcium 75 200 75 200
Magnesium 50 150 50 150
Iron 0.30 1.00 0.30 1.00
Manganese 0.10 1.50 0.10 1.50
Copper 1.00 1.50 1.00 1.50
Zinc 5 15 5 15
Chloride 200 600 250 1000
Sulphate 200 400 250 400
Magnesium + Sodium Sulphate 500 1000 - -
Phenolic substances (as phenol) 0.001 0.002 0.001 0.002
Flouride - 1.5 1.0 2.0
Nitrate Nitrogen - 45 20 50
Nitrite Nitrogen - - - -
Carbon Chloroform extract (CCE-Organic Pollutants) 0.20 0.50 - -
Alkyl benzoyal sulphonates (ABS Sulphactants (ms/l) 0.50 1.00 - -
Toxic: Cadmium - 0.01 - -
Chromium (as Hexavelent) - 0.05 - 0.01
Cynaide - 0.20 - 0.01
Arsenic - 0.05 - 0.20
Lead - 0.05 - 0.10
Selenium - 0.01 - 0.05

The rain water is the purest form of water. Therefore, the rain water collected from neat and clean surfaces like terrace can be directly used. It is advisable to filter and boil the water so collected as when it runs on the surface source dust particles may come with it.

Soil Lithology and Rain Water Harvesting

The quantum of the rain water which can be harvested are recharged into the underground aquifer depends on the nature of the soil. The design of the RWH structures depends on the soil nature. If the soil is having good permeability, water will be recharged fast but if the permeability of the soil is poor, the water recharge will be very slow. For example, the permeability of sandy soil is good and of clay is poor. Therefore, it can be seen that the water drains/seeps underground very fast while in clay it is very slow.

Therefore the RWH structure is to be designed in such a way that through recharge pits/bores the water is taken upto sandy strata so that the rate of percolation is fast.

The map below indicates various soil zones in Chennai city and the desired depth of the RWH structures.

Details of favourable aquifer zones

SI.NO Colour Selected Areas Water level during summer in 'm' Depth of the aquifer in 'm' Saturated thickness in 'm' Recharge zone in 'm'
1. Blue Secretariat, Port,Chepauk, Triplicane,Santhome Seashore, Karpagam Garden, M.R.C. Nagar 3 10 7 3
Egmore, BesantNagar SasthriNagar, Karpagam Avenue, Thiruvanmiyur 4 10 6 4
Ekkattuthangal 6 10 6 4
2. Orange ParrysCorner, Mint,Sevenwells, Kothaval Chavadi, VallalarNagar, ParkTown, Sowcarpet, Mylapore, Mandaiveli, Alwarpet, RajaAnnamalapuram, Pattinapakkam 6 5 9 6
3. Yellow Nungambakkam(Lakearea), T.Nagar, West CITNagar, Teynampet, Gopalapuram, Royapettah, ThousandLights, KK Nagar 9 15 6 9
Adayar,GandhiNagar, IndiraNagar, Kasthuribha Nagar 8 15 7 8
4. Light Red Ayanavaram, ICFQuarters, Kilpauk, Kilpauk Garden, Shenoy Nagar(East) 7 20 13 7
Anna Nagar, Anna Nagar (West), Shenoy Nagar (West) 12 20 18 12
Koyambedu 14 30 16 14
5. Green Perambur 7 30 23 7
Alandur,Guindy, Chinnamalai, Tharamani, St.Thomas Mount Hard Rock

The following table shows the porosity, specific yield and permeability characteristics of soil formation.

Representative Values for Selected Soil Formation

SI.NO Description Porosity Percent Specific Yield Percent Permeability gallon per day/sq.ft.
1. Clay 45 - 55 1 - 10 0.011 - 2.0
2. Sand 35 - 40 10 - 30 100 - 3000
3. Gravel 30 - 40 15 - 30 1000 - 15000
4. Sand and Gravel 20 - 35 15 - 25 200 - 5000
5. Sandstone 10 - 20 5 - 10 0.1 - 50
6. Shale 1 - 10 0.5 - 5 0.00001 - 0.1
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