Issue: a new reservoir for water supply

Model answer

A - removing salt from sea water or estuary water to make fresh water.

Model answer

Desalination uses a lot of energy to force salty water through membranes to remove the salt. This means it has high running costs, which push up water bills, and if the electricity comes from fossil fuels it releases greenhouse gases that add to climate change.

Model answer

Some people in Wales feel that water is a Welsh resource that is being taken to benefit people elsewhere. There is a long history of resentment: in the 1960s the village of Capel Celyn was flooded to create a reservoir for Liverpool. People may also worry that in a long drought Wales and the Severn area would run short of water themselves, yet still be expected to send water to the south-east. Along the River Severn, changing the flow by releasing and removing large amounts of water could harm salmon and other wildlife, and moving water between catchments can spread invasive species. Building a 200 km pipeline would also disrupt farmland and the countryside along the route.

Model answer

A sustainable water supply meets people's needs today without harming the environment or the ability of future generations to meet their needs, at a cost society can afford.

Much of Option 3 is very sustainable because it reduces the amount of water people need instead of taking more from the environment. About 60 of the 100 Ml/d would come from saving water. Fixing leaks to cut leakage from 20% to 12% would save 35 Ml/d of water that has already been treated and pumped, saving energy as well as water. Compulsory meters would reduce use by about 15% per person, because people pay for what they use, and they encourage people to value water in the long term. Grey-water recycling reuses water instead of wasting it. None of these measures floods a valley or takes water from another region, so rivers and chalk streams in the south-east would be under less pressure, and the savings would start soon, from 2027.

The desalination plant is less sustainable. It does have the great advantage of not depending on rainfall, so it would still work in a long drought or as summers become drier with climate change. However, it uses large amounts of energy, which means greenhouse gas emissions unless renewable electricity is used, and its salty waste could harm wildlife in the estuary.

There are also social and economic concerns. Running costs of about £18 million a year are high and could push up bills, and compulsory meters could hit large families and people on low incomes hardest, causing water poverty unless there are special tariffs. Finally, the 100 Ml/d is only achieved if all the targets are met, and leakage and behaviour targets are often missed.

Overall, Option 3 is sustainable to a large extent, because most of the water comes from using water more efficiently, which benefits the environment and future generations. Its sustainability is reduced by the energy use and brine of the desalination plant and its effect on poorer households, so it would be more sustainable if the plant used renewable energy and help were given to struggling families.