VPE 511: Environment and Environmental Hygiene (2+1)

CHLORIDES

• Chlorides are rarely absent from natural waters, being present chiefly as sodium chloride, with occasionally magnesium, potassium and calcium chlorides.
• The chloride content of waters derived from rocks near the sea is invariably high; waters from deep wells may contain sufficient to impart a brackish taste.
• The presence of chloride considered alone is therefore of little significance as regards hygienic quality, but as sewage contains appreciable quantities of it, if the chloride is present together with free ammonia, nitrite or appreciable quantities of nitrate, this finding may support an indication of sewage pollution.
• Uncontaminated surface waters (except near the sea ) rarely contain more than 2 parts of chloride per 100,000; well waters may contain considerably greater quantities.