Skip to main content

Types of impurities in water

Short answer

Impurities are substances in water other than H2O, classified by size as suspended (above 1 micron), colloidal (1 nm to 1 micron), and dissolved (below 1 nm). By characteristics they are physical, chemical, and biological, and also organic or inorganic. Removal methods include screening, sedimentation, coagulation, filtration, aeration, and special treatment.

Define impurities in water and describe briefly the types of impurities present in water (according to their characteristics and state).

Impurities are the substances (physical, chemical or biological) present in water other than H2O molecules. Natural water picks up impurities from the atmosphere, the ground, and human and animal activity.

According to state (size)

TypeSizeExamplesEffectsRemoval
SuspendedAbove 1 micron (0.001 mm)Sand, silt, clay, algae, protozoa, bacteriaTurbidity, disease, siltingScreening, sedimentation, filtration
Colloidal1 nm to 1 micronFine clay, silica, colour-causing humic matter, virusesColour, turbidity, does not settleCoagulation, flocculation, filtration
DissolvedBelow 1 nm (ionic or molecular)Salts of Ca, Mg, Na, Fe, Mn; gases (CO2, H2S, O2); organic matterHardness, taste, odour, toxicitySoftening, aeration, ion exchange, adsorption, special treatment

According to characteristics

  • Physical: turbidity, colour, taste, odour, temperature.
  • Chemical: pH, hardness, alkalinity, chloride, sulphate, iron, manganese, nitrate, fluoride, arsenic, dissolved gases, toxic metals.
  • Biological: bacteria, viruses, protozoa, algae, helminths and other living organisms, some of which cause disease.

Impurities are also grouped as organic (plant, animal and sewage matter) and inorganic (minerals and salts).

✓ Answer checked by Claude Opus 5.5 (high effort)

Related questions

All Water Supply Engineering chapter 4 questions →