Overview
This lecture explains what potable (drinkable) water is, criteria it must meet, sources of potable water, and how it is treated—including desalination methods for seawater.
What is Potable Water?
- Potable water is water that is safe to drink but is not necessarily chemically pure.
- Pure water in chemistry only contains H2O molecules, while potable water may have dissolved substances.
- Three criteria for potable water: low levels of dissolved substances, pH between 6.5 and 8.5, and no microorganisms.
Sources of Potable Water
- Most countries rely on fresh water sources, which have few dissolved substances.
- Fresh water comes from rain, which collects as either surface water (lakes, rivers, reservoirs) or groundwater (aquifers underground).
- Surface water is easy to access and frequently replenished by rain but may dry up in hot climates.
- Groundwater is used more in areas where surface water is scarce.
Treating Fresh Water
- Fresh water is filtered through wire mesh to remove large debris.
- It is then filtered through sand and gravel to remove smaller solid particles.
- The water is sterilized (to kill microbes) by bubbling chlorine gas, using ozone, or exposing it to ultraviolet light.
Desalination of Seawater
- Desalination provides potable water from seawater when fresh water is scarce (e.g., in some Middle Eastern countries).
- The two main desalination methods are distillation (boiling and condensing water vapor) and reverse osmosis (passing water through a membrane).
- Both methods produce pure water but require large amounts of energy and are expensive.
Key Terms & Definitions
- Potable water — Water that is safe to drink.
- Fresh water — Water with low levels of dissolved substances.
- Surface water — Water from exposed sources like lakes and rivers.
- Groundwater — Water stored underground, often in aquifers.
- Desalination — Process of removing salt and other substances from seawater to make it potable.
- Distillation — Heating water to produce vapor and condensing it to separate out pure water.
- Reverse osmosis — Forcing water through a membrane so only water molecules pass, removing impurities.
Action Items / Next Steps
- Review treatment steps for potable water.
- Understand and compare distillation and reverse osmosis.
- Study the criteria for potable water in preparation for exams.