Sulphates:

Presence of sulphates in water may be from different sources. Dissolution of gypsum and other mineral deposits containing sulphates from oxidation of sulphides, sulphites and from industrial effluents is the main cause. Sulphates in water contribute permanent hardness. High level of sulphates concentration imparts taste and if combined with magnesium and sodium has a laxative effect. Bacterial reduction of sulphates under anaerobic conditions produces hydrogen sulphide, which is an objectionable gas smelling like rotten eggs, which could be reduced with the help of aeration.