76. Potable Water

1. What is Potable Water?

Potable water is water that is safe to drink. In chemistry, "pure" water contains only H2O molecules, but potable water often contains dissolved substances. To be considered potable, water must meet three criteria:

• Dissolved substances: Levels must be fairly low.

• pH levels: Must be between 6.5 and 8.5 (neither too acidic nor too alkaline).

• Microorganisms: Must be free of harmful bacteria or fungi.

2. Treating Fresh Water

Most potable water comes from fresh water sources like surface water (lakes, rivers, reservoirs) or ground water (aquifers). The treatment process generally involves three steps:

• Filtration (Large): Water is passed through a wire mesh to remove large objects like twigs.

• Filtration (Small): Water is passed through a bed of sand and gravel to filter out smaller solid particles.

• Sterilization: To kill harmful microbes, the water is treated using one of three methods:

  • Bubbling chlorine gas through it.

  • Exposing it to ozone.

  • Exposing it to ultraviolet (UV) light.

3. Desalinating Seawater

In areas with little fresh water, potable water is produced from seawater through desalination. While seawater is a limitless supply, these processes are very expensive because they require vast amounts of energy.

• Distillation: Salty water is boiled; the steam is collected and condensed to form pure water, leaving the salt behind.

• Reverse Osmosis: Salty water is passed through a membrane that only allows water molecules to pass through, trapping salt ions and larger molecules on the other side.

Summary Comparison