The most important salt found in sea water is sodium chloride (NaCl), widely
used for domestic and culinary purposes, but there are plenty more. The salinity
of water, i.e. the quantity of salts in the water, is expressed in 0/00 or in g/liter.
The mean salinity of the Earth's oceans is around 350/00, or approximately 35 g
salts/liter. Whatever its salinity, sea water boasts one remarkable property: the
proportion of each element is constant.
Desalinated water does not therefore contain less of one or more salts, but the
combination of salts is present in a lower concentration.
The salinity of sea water varies according to longitude. It is at its highest
in open seas in the tropics, it is lower near coasts and after heavy rain, and it
is at its lowest near the poles (due to the influence of melting snow).