Potable water Flashcards – AQA GCSE Combined Science: Trilogy (8464) — Chemistry — Higher

What is potable water?

Water that is safe to drink.

What two types of substance or organism must be present at sufficiently low levels in potable water?

Dissolved salts and microbes.

How does potable water differ from chemically pure water?

Pure water contains only $\ce{H2O}$ molecules and no dissolved substances. Potable water can contain dissolved minerals and gases at safe levels.

What is desalination?

The removal of dissolved salts from salty water or seawater to produce potable water.

What are two methods of desalination?

Distillation and membrane processes, such as reverse osmosis.

How does distillation desalinate water?

Water is evaporated and then condensed, leaving most dissolved salts behind.

How does reverse osmosis desalinate water?

Water is forced through a membrane that lets water molecules pass but blocks many dissolved ions and other substances.

What is a major energy requirement of desalination methods?

They require large amounts of energy.

Rank groundwater, wastewater and salt water from generally easiest to hardest to make potable.

Groundwater → wastewater → salt water.

Why is groundwater usually the easiest source to make potable?

Rocks naturally filter it, so it often needs less treatment to remove dissolved substances and microbes.

Why does wastewater require substantial treatment to become potable?

It contains sewage, organic matter, microorganisms and other contaminants.

Why is salt water generally the hardest source to make potable?

Dissolved salts must be removed by desalination, which is energy-intensive and expensive; other impurities may also need treatment.

What two factors should be compared when assessing how difficult water sources are to make potable?

The starting level of contamination and the amount of treatment needed to make the water safe to drink.