Chemistry · Ch 14 — Environmental Chemistry
International Standards for Drinking Water
14.3.2
International Standards for Drinking Water
Fluoride
Fluoride concentration in drinking water must be monitored carefully because both too little and too much cause harm.
- Deficiency causes tooth decay. Soluble fluoride is deliberately added to bring the concentration up to about 1 ppm (1 mg dm⁻³). Fluoride ions harden tooth enamel by converting hydroxyapatite, , into the much harder fluorapatite, .
- Excess fluoride above 2 ppm causes brown mottling of teeth, and levels above 10 ppm damage bones and teeth — a problem documented in parts of Rajasthan.
Lead
Drinking water becomes contaminated with lead when it passes through lead pipes. The prescribed upper limit is about 50 ppb. Lead exposure can damage the kidneys, liver and reproductive system.
Sulphate
Sulphate concentration above 500 ppm has a laxative effect; at moderate levels it is harmless.
Nitrate
The maximum permissible nitrate level is 50 ppm. Excess nitrate in drinking water can cause methemoglobinemia, commonly known as 'blue baby' syndrome.
Other Metals — Maximum Prescribed Concentrations
| Metal | Maximum concentration (ppm or mg dm⁻³) |
|---|---|
| Fe | 0.2 |
| Mn | 0.05 |
| Al | 0.2 |
| Cu | 3.0 |
| Zn | 5.0 |
| Cd | 0.005 |
What Individuals Can Do
- Check local water sources' pH and report pollution to the Pollution Control Board.
- Never dump household or industrial waste directly into drains that lead to rivers, ponds or lakes. …
Table 14.2Maximum Prescribed Concentration of Some Metals in Drinking Water.
| Metal | Maximum concentration (ppm or mg dm–3) |
|---|---|
| Fe | 0.2 |
| Mn | 0.05 |
| Al | 0.2 |
| Cu | 3.0 |