Chemistry · Ch 15 — Environmental Chemistry
Quality of Drinking Water
Quality of Drinking Water
Many of us now hesitate to use natural water directly for drinking, because biological, physical or chemical impurities from different sources mix with surface water or ground water.
Institutions like the WHO (World Health Organisation) at the world level, and the BIS (Bureau of Indian Standards) and ICMR (Indian Council of Medical Research) at the national level, have prescribed standards for the quality of drinking water. The standard characteristics prescribed by BIS, in 1991, for deciding the quality of drinking water are shown below.
| S.No | Characteristics | Desirable limit |
|---|---|---|
| I. Physico-chemical Characteristics | ||
| i) | pH | 6.5 to 8.5 |
| ii) | Total Dissolved Solids (TDS) | 500 ppm |
| iii) | Total Hardness (as CaCO₃) | 300 ppm |
| iv) | Nitrate | 45 ppm |
| v) | Chloride | 250 ppm |
| vi) | Sulphate | 200 ppm |
| vii) | Fluoride | 1 ppm |
| II. Biological Characteristics | ||
| i) | Escherichia Coli (E. coli) | Not at all |
| ii) | Coliforms | Not to exceed 10 (in 100 ml water sample) |
| S.No | Characteristics | Desirable limit |
|---|---|---|
| I. Physico-chemical Characteristics | ||
| i) | pH | 6.5 to 8.5 |
| ii) | Total Dissolved Solids (TDS) | 500 ppm |
| iii) | Total Hardness (as CaCO₃) | 300 ppm |
| iv) | Nitrate | 45 ppm |
| v) | Chloride | 250 ppm |
| vi) | Sulphate | 200 ppm |
| vii) | Fluoride | 1 ppm |
| II. Biological Characteristics |
Fluoride
Fluoride ion deficiency in drinking water causes tooth decay. Water-soluble fluorides are added to drinking water to increase the fluoride-ion concentration up to 1 ppm.
Fluoride ions make the enamel on teeth much harder, by converting hydroxyapatite, [3(Ca₃(PO₄)₂)·Ca(OH)₂] -- the natural enamel on the surface of teeth -- into the much harder fluorapatite, [3(Ca₃(PO₄)₂)·CaF₂]. …
Lead
Drinking water containing lead contamination above 50 ppb can cause damage to the liver, kidney and re …
Sulphate
A moderate level of sulphate is harmless. But an excessive concentration -- above 500 ppm -- of sulphates in drinking water ca …
Nitrate
Use of drinking water having a nitrate concentration higher than 45 ppm may cause methemoglobinemia (blue baby syndrome), a disea …
Total Dissolved Solids (TDS)
Total dissolved solids (TDS). Most salts are soluble in water. TDS includes cations like calcium, magnesium, sodium, potassium and iron, and anions like carbonate, bicarbonate, chloride, sulphate, phosphate and nitrate. Use of drinking water having a TDS concentration higher than 500 ppm causes the p …