Potable Water

Drinking Water

• Drinking water is essential for human life, but not all water is safe to drink.

• Safe drinking water must have:

  • Low levels of dissolved salts (e.g. sodium chloride).

  • Low levels of microbes (e.g. bacteria).

• Potable $\ne$ Pure

• Potable water = water that is safe to drink.

• Pure water = contains no dissolved substances at all.

• Potable water often contains small amounts of dissolved substances.

Production of Potable Water (UK example)

1. Source – rainwater (low levels of dissolved substances) collects in:

   • Aquifers (underground).

   • Lakes, rivers, reservoirs.

2. Filtration – water passed through filter beds to remove:

   • Leaves.

   • Suspended particles.

3. Sterilisation – to kill microbes.

   • Chlorine (used in the UK).

   • Some countries use ozone or ultraviolet light.

Producing Potable Water from Salty Water

• In many countries, fresh water is scarce.

• Seawater contains very high levels of dissolved minerals.

• Potable water can be produced by desalination:

  • Distillation (boiling → condensing water).

  • Reverse osmosis (passing through membranes).

• Both methods reduce dissolved minerals to safe levels.

• Both require large amounts of energy, so are very expensive.

✅ Key Idea:

• Potable water ≠ pure water.

• Potable water contains low levels of dissolved substances but is safe to drink.

• Methods depend on the source:

  • Fresh water → filter + sterilise.

  • Salty water → desalination (distillation or reverse osmosis).