Potable Water – IGCSE Chemistry Definition
IGCSE Chemistry definition of potable water: water safe to drink. Covers treatment steps, chlorination, and exam tips for Cambridge 0620.
Published by IGCSEChemistry.com.my
Chemistry teaching team: K. S. Tan (15+ years teaching IGCSE Chemistry) and Ms Yash (10+ years teaching IGCSE Chemistry) and Ms Kartini (15+ years teaching IGCSE Chemistry).
Mapped to Cambridge IGCSE Chemistry 0620 (2026–2028). Last updated 2026-08-19.
Potable water appears in the environmental chemistry section of the 0620 syllabus. The examiner expects you to distinguish potable water from chemically pure water and to describe the treatment steps that make raw water safe to drink.
The 0620 definition
Potable water is water that is safe for drinking. It has sufficiently low levels of dissolved salts and microorganisms to be safe for human consumption.
Potable water is not chemically pure — it contains dissolved minerals (calcium, magnesium salts) and dissolved gases, but these are at safe concentrations.
Treatment of water to make it potable
| Step | Purpose |
|---|---|
| Sedimentation | Large particles settle to the bottom of a tank |
| Filtration through sand/gravel beds | Removes smaller insoluble particles |
| Chlorination | Kills bacteria and other microorganisms |
Some water treatment works also use:
- Activated carbon filters to remove taste and odour compounds
- pH adjustment to reduce corrosion of pipes
- Fluoridation (addition of fluoride) to reduce tooth decay
Why chlorination is used
Chlorine is added in small amounts to kill pathogenic bacteria and viruses. It remains in the water supply at low concentration to prevent recontamination during distribution through pipes. This is called a residual disinfectant.
Potable water from seawater
In regions with limited freshwater, seawater can be made potable by desalination:
- Distillation: boil seawater, condense the steam — energy-intensive
- Reverse osmosis: force seawater through a membrane that allows water molecules through but blocks dissolved salts
Both methods are more expensive than treating freshwater, which is why desalination is mainly used in desert regions.
Worked exam question
Describe how river water is treated to produce potable water. [3]
Mark scheme
Sedimentation / allowing large particles to settle [1]; filtration through sand or gravel beds to remove insoluble particles [1]; chlorination / adding chlorine to kill bacteria / microorganisms [1]
Common exam mistakes
- Saying potable water is “pure water” — it is safe water, not chemically pure H₂O.
- Describing distillation as the standard method for making drinking water — distillation is used for desalination, not for treating freshwater.
- Forgetting the purpose of each step — sedimentation removes large particles, filtration removes small particles, chlorination kills microorganisms.
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