Water Purity

Water is needed for drinking, and domestic uses such as washing.

Industrially it is important as a cheap raw material, a coolant (power stations) and solvent.

Between a half and two thirds of all frsh water used in UK is industrial.

In the UK, water gotten from:

• Surface water - lakes, rivers, reservoirs (artificial lakes). Much of England and Wales, resources start running dry in summer months.
• Groundwater - aquifers (rocks that trap water underground). South-east where surface water very limted, as much as 70% of domestic water supply is groundwater.

All resources limited and depend on annual rainfall and demand for water increases every year. Experts worry that unless we limit water use, by 2025 not enough water to supply everyone's needs so important to conserve.

How much purification needed depends on source. Groundwater from aquifers usually quite pure but surface water needs lots of treatment. Processes:

1. Filtration - wire mesh screens out large twigs and gravel and sand beds filter out other large bits.

2. Sedimentation - iron sulphate or aluminium sulphate added to water which makes fine particles clump and settle.

3. Chlorination - chlorine gas bubbled through to kill harmful bacteria and other microbes.

Some soluble impurites dissolved in water not removed because cannot be filtered out. Includes minerals that makes water hard and other harmful/poisonous chemicals such as pesticides and fertilisers.

Water out of taps have to meet strict safety standards but low levels of pollutants still found from various sources:

• Nitrate residues from excess fertiliser run-off into rivers and lakes. Too much nitrate in drinking water can cause serious health problems, especially for babies, nitrates prevent blood carrying oxygen properly.
• Lead compounds from old lead pipes, lead poisonous especially for children.
• Pesticide residues - spraying too near rivers and lakes.

Can get fresh tap water by distilling seawater. In dry countries, sea water distilled for drinking water. Needs a lot of energy so really expensive and not practical for large quantities of fresh water.