Types of Impurities in Water | Engineering Chemistry Notes

Types of Impurities in Water

Water found in nature is never chemically pure. It contains different kinds of impurities that influence its quality, suitability for drinking, and industrial usage. These impurities can broadly be classified into three categories: Physical, Chemical, and Biological impurities.

1. Physical Impurities

These impurities alter the physical appearance and properties of water.

Suspended solids: Sand, clay, silt.
Color: Due to organic matter, algae, or industrial effluents.
Turbidity: Caused by suspended particles.
Taste and odor: From decaying matter, dissolved gases (H₂S), or algae.
Temperature: Elevated due to industrial discharge or natural conditions.

2. Chemical Impurities

These are dissolved substances that change the chemical nature of water. They may be inorganic or organic in origin.

Dissolved gases: CO₂ (causes acidity), O₂ (enhances corrosion), H₂S (bad odor).
Inorganic salts:
- Ca²⁺, Mg²⁺ → Hardness of water
- Na⁺, K⁺, Cl^-, SO₄^2- → Salinity
- Fe²⁺, Mn²⁺ → Staining and taste issues
Organic compounds: Agricultural pesticides, industrial effluents, natural organic matter.
Toxic chemicals: Heavy metals like Pb, As, Hg.

3. Biological Impurities

These include living microorganisms that contaminate water and cause health issues.

Bacteria: E. coli (indicator of fecal contamination), Vibrio cholerae (cholera).
Viruses: Hepatitis virus, Polio virus.
Protozoa: Giardia, Entamoeba histolytica (amoebic dysentery).
Algae: Cause taste, odor, and oxygen depletion.

Figure: Classification of impurities in water

Examples of Each Type

Type	Examples	Main Effect
Physical	Sand, silt, color, odor	Turbidity, unpleasant taste/appearance
Chemical	Ca²⁺, Mg²⁺, CO₂, pesticides	Hardness, corrosion, toxicity
Biological	Bacteria, viruses, protozoa, algae	Diseases, taste/odor issues