Obtaining potable water

In a nutshell

During periods of drought, potable water cannot be obtained by precipitation and we, therefore, rely on desalination to make seawater potable. Desalination can occur in many ways, including thermally or via reverse osmosis.

Drought

Droughts occur when there isn't enough precipitation and it can cause huge issues due to our reliance on precipitation for fresh drinking water. During a drought, we can obtain water suitable for drinking (potable water) via methods such as desalination.

Desalination

Desalination is the process of removing salts from salt water, such as seawater. There are different methods of desalination including thermal desalination and reverse osmosis.

Thermal desalination

1.	Saltwater is boiled in a large enclosed vessel.
2.	This causes water to evaporate.
3.	The steam rises to the top of the vessel whilst the water remains at the bottom.
4.	The steam travels down a pipe from the top of the vessel and then condenses into pure water.

Reverse osmosis

Normal osmosis is the net movement of water across a partially permeable membrane from an area of high water concentration to an area of low water concentration. Reverse osmosis will be the opposite: the net movement of water across a partially permeable membrane from an area of low water concentration to an area of high water concentration.

Biology; Ecosystems and material cycles; KS4 Year 10; Obtaining potable water — 1. Reverse osmosis, 2. Normal osmosis, 3. Pressure, A. Pure water, B. Salt water.

i	Saltwater is treated to remove any solids.
ii	It is then fed into a vessel at very high pressure. The vessel contains a partially permeable membrane.
iii	This high pressure causes water molecules to move in the opposite direction to normal osmosis. They move from an area of low water concentration (but high salt concentration) to an area of high water concentration (but low salt concentration).
iv	As the pressure forces the water through the membrane, salts are left behind and this desalinates the water.