C6.3 water treatment

Where do we get our water from in the uk?

• surface water: lakes, rivers and reservoirs

• Ground water: aquifers (rocks trap water underground)

• Note: you can get clean water by treating wastewater (remove contaminants)

What does the availability of water defend on?

Annual rainfall

The demand for water increases every year so we must conserve water where possible

what is ‘portable’ water?

Water that is safe to drink

What is the difference in purity between ground water and surface water?

• Ground water from aquifers is usually quite pure.

• Surface water needs treatment (may contain insoluble material, microorganisms, fertilisers and pesticides)

Describe how fresh water is treated to make it safe to drink?

• Filtration - wire mesh removes large twigs. Sand/gravel beds filter out any other solid bits e.g leaves

• Sedimentation - iron sulphate and aluminium sulphate is added to the water. This causes the fine particles to clump together

• Chlorination - chlorine gas is bubbled through to kill harmful bacteria and other microbes. Can use UV and ozone too. Sterilisation

Describe how salt water is treated to make it safe to drink

Process - desalination

Methods:

• distillation - separates mixtures with different boiling points. (Larger small scale)

• Reverse osmosis (used for small scales)

What does tap water contain?

Water has to meet strict safety standards. It does contain small levels of pollutants.

it contains:

• nitrate residues (from fertiliser run-off)

• Lead compounds (lead pipes)

• Pesticide residues

What does waste water mainly contain?

Large amounts of organic molecules (from urine and faeces). Also harmful organisms