Sources of water
Water is obtained from rain, rivers, lakes, springs, wells, boreholes, and reservoirs. Groundwater is often filtered naturally as it passes through soil and rock, but it can still be contaminated by sewage, chemicals, or nearby waste.
Impurities in water
- Suspended impurities: soil, clay, and plant material.
- Dissolved salts: mineral ions and other dissolved substances.
- Microorganisms: bacteria, viruses, and parasites.
- Organic pollutants: sewage, oil, and decaying material.
Hardness of water
Hard water contains dissolved calcium or magnesium ions. It does not lather easily with soap and may form scale in kettles and pipes. Temporary hardness can be reduced by boiling, while some permanent hardness requires chemical treatment or ion exchange. Hard water can provide useful mineral ions, but scale may reduce efficiency in equipment.
Purification
- Screening and sedimentation: remove large particles and allow suspended material to settle.
- Filtration: passes water through a medium that traps particles.
- Boiling: kills many disease-causing microorganisms.
- Disinfection: controlled chlorination or another approved method reduces pathogens.
- Further treatment: may include aeration, activated carbon, distillation, or membrane processes depending on the impurity.
Safe water practice
Store treated water in clean, covered containers and avoid dipping dirty cups or hands into it. Protect wells and water sources from latrines, refuse, animals, and chemical contamination.
Revision questions
- Name four sources of water.
- State four types of impurities in water.
- Why is hard water troublesome when washing?
- Describe three water-purification methods.
