What are the common impurities mostly found in natural water?

Impurities in water are classified into three heads

  • Suspended impurities
  • Colloidal impurities
  • Dissolved impurities
  • Suspended impurities

These impurities are dispassion of solid particles that are large enough to be removed by filtration on the surface and heavier ones settle down. The suspended particles which have the same specific gravity as that of water are mixed in the water suspended impurities include, clay, algae, organic and inorganic matter and mineral matter etc. these all impurities are macroscopic and cause turbidity in the water.

The following are the effects of suspended impurities

  • Bacteria some cause disease
  • Algae protozoa-cause colour, turbidity and odour
  • Clay, silt-cause turbidity
  • Colloidal impurities

It is very finely divided dispersion of particle in water. These particles are so small cannot be removed by ordinary filters and are not visible to the naked eye. As a matter of fact, all the colloidal impurities are electrically charged and remain in continuous motion. The electric charge is due to the presence at absorbed ions on the surface at solid due to repelling action all the particles remain in motion and do not settle that is why their removal is very difficult. These colloidal impurities are generally associated with organic matter containing bacteria and are the chief source of epidemics.

Dissolved impurities

Some impurities are dissolved in water when it moves over the rocks, soil etc. solids, liquid and gases are dissolved in natural water. These dissolved impurities may contain the organic compound, inorganic salts and gases etc. the concentration of total dissolved solids is usually expressed in p.p.m and is obtained by weighing the residue after evaporation of water sample from a filtered sample.

The following are effects of dissolved impurities

  • Suspended impurities
  • Bacteria – some cause disease
  • Algae, protozoa-cause odour, turbidity and colour
  • Clay, silt – cause turbidity
  • Dissolved impurities

Calcium and magnesium
{carbonate – cause hardness and alkalinity
{Sulphate – cause hardness
{Bicarbonate – cause alkalinity and hardness
{fluorides – cause mottled enamel of teeth
{chloride – taste and salinity
{Manganese – blank or brown colour
{Iron oxide – taste, corrosiveness, hardness and colour
{lead – cause poisoning
{Arsenic – poisoning
{Oxygen – corrode the metals
{Carbon – dioxide – cause acidity and corrode the metal
{Hydrogen sulphate – cause rotten – egg odour, acidity and corrode
The metals Organic impurities
{Vegetable – colour, taste and acidity
{Animal – produce harmful disease germs{[Dead]
{Vegetable – produce bacteria’s
{animal – cause pollution of water and produce
{disease germs

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