Drinking water

What must potable water have?

Low levels of contaminating substances and low levels of microbes.

Where can fresh water come from and what does it likely contain?

Reservoirs, lakes and rivers. It us likely to contain objects such as leaves or twigs, insoluble solids such as particles of soil and microbes, which may cause disease.

Tap water is potable but is not a pure substance. What does it contain?

Dissolved salts and dissolved chlorine

What are the main stages during water treatment?

1) Sedimentation 2) Filtration 3) Chlorination

What happens during sedimentation for the water treatment?

Large insoluble particles sink sink to the bottom a tank

What happens during filtration for the water treatment?

Small insoluble particles are removed by filtering through beds of sand.

What happens during chlorination for the water treatment?

Chlorine gas is bubbled from the water to kill microbes.

Sea water contains dissolved salts. Their concentration is too high to drink it safely. How can this sea water become safe to drink?

Sea water can be made potable by simple distillation: Filtered sea water is boiled . The water vapour is cooled and condensed to form distilled water.

What does distilled water contain and not contain?

Distilled water does not contain dissolved salts but it contains dissolved gases from the air.

Give a positive of simple distillation of sea water

•Uses a plentiful raw material •Produces pure water •Kills microbes in sea water

Give a negative of simple distillation of sea water

Needs a lot of energy to heat the water.