Artificial Quiescent Water as in Impounding Reservoirs:

Impounding reservoirs are formed by the construction of hydraulic structures across the river/stream. In general, water of these reservoirs have less pollution as compared to flowing streams because of settling of solid matters (except colloidal clays) in its relatively quiescent water. The water stored in impounding reservoirs are normally designed for multipurpose schemes and operated so as to get optimum benefits.

The growth of vegetation normally occurs on the top layers of large impounding reservoirs. Vegetation undergoes decay and adds an extra load on natural purification processes. Colour may be added from leaching of vegetable tannins and the subsequent oxidation of these substances to compounds of dark brown colour. Removal of vegetation from time to time is, therefore, essential.

Sea Water

Extracting potable water from sea is a very costly affair. However, it is adopted in the situation where there is no alternative source of water (such as ships on the high sea etc.) is available.