Salinity indicates the concentration of salts in a solution: while in the past salinity was determined by chlorinity, a quantity that expresses the total content of chlorides (Cl–), bromides (Br–) and iodides (I–), today the officially adopted unit of measurement is based on electrical conductivity, which takes better account of all the salts in solution.
Salinity is an ecological factor of considerable importance, capable of influencing the type of organisms living in a body of water. Salinity affects the types of plants that can grow in an aquatic environment or in soil that is washed by water. A plant adapted to saline conditions is called a halophyte. Organisms (mainly bacteria) that can live in very salty conditions fall into the category of extremophiles, or more specifically, halophiles. An organism capable of living in a wide range of salinity is called an euryhaline.
The salt content of water is an important factor in determining the potability of water or its potential use for industrial or agricultural purposes. Salt removal is not easy and also requires some energy expenditure.