Desalination is the process of removing salt and other minerals from water. The process is most commonly used to make seawater or brackish water drinkable, but it can also be applied to obtain ultrapure water that far exceeds drinking water requirements, for certain industrial processes.
The greater the salinity of the feedwater and the greater the purity of the product water, the greater the energy required in the desalination process. Salinity is defined according to the total dissolved solids (TDS). This is measured in milligrams per litre (mg/l) or parts per million (ppm). The two units are generally interchangeable in dilute solutions, although ppm is used more commonly in the US.
- Seawater: 15,000-50,000 mg/l TDS
- Brackish water: 1,500-15,000 mg/l TDS
- River water: 500-3,000 mg/l TDS
- Pure water: less than 500 mg/l TDS
The total contracted capacity in the desalination market by feedwater category is shown in the figure below.