Impurities in Water

Impurities in Water

• Chemically pure water is composed of two parts hydrogen and one part oxygen.

• Natural water contains various impurities categorized as suspended matter, dissolved substances, colloidal impurities, and organic impurities.

Suspended Matter

• Inorganic suspended matter includes clay and sand.
• Organic suspended matter includes animal and vegetable matter.

Dissolved Substances

• Inorganic salts include carbonates, chlorides, and sulfates of calcium & magnesium.
• These salts cause water hardness.
  • Calcium & magnesium bicarbonates dissolve in water when it passes through dolomite or limestone in the presence of air.
  • CaCO₃ + H₂O + CO₂ → Ca(HCO₃)₂
  • MgCO₃ + H₂O + CO₂ → Mg(HCO₃)₂
• Dissolved gases in water include CO₂, N₂, O₂, and H₂S.
  • CO₂, N₂, O₂, and H₂S can cause odor and acidity.
  • O₂ can also cause corrosion in boilers.
• Other dissolved salts include sodium, potassium, iron, manganese, silica, and alumina.
  • Some trivalent cations like Fe and Al may be present.

Colloidal Impurities

• Finely divided substances not visible to the naked eye.
• Includes silica, clay, aluminum hydroxide, and microorganisms.
• Can cause color, odor, and diseases.

Organic Impurities

• Includes algae, fungi, plant matter, and microorganisms (bacteria being animal in origin).

Sources of Impurities

• Rainwater floods carry floating impurities.
• Atmospheric gases like CO₂, O₂, etc. are absorbed into water.
• Water percolating through the soil dissolves salts like calcium, magnesium, and sodium.
• Decomposition of organic matter from plant and animal remains, sewage, and industrial waste introduce organic impurities.

Effect of Impurities

Domestic Purposes

• Hardness caused by dissolved salts of calcium and magnesium prevents soap from forming lather.
• Soap is essentially a mixture of sodium and potassium salts of higher fatty acids.