Salinity refers to the saltiness or amount of salt dissolved in a body of water, such as saline water

. It is usually measured in g/L or g/kg (grams of salt per liter or kilogram of water) and is a crucial factor in determining many aspects of the chemistry of natural waters and biological processes within them

. Salinity is also a thermodynamic state variable that governs physical characteristics like the density and heat capacity of the water

. Salinity is important for several reasons:

• It can affect the health, environmental, and economic aspects of water bodies, making water unsuitable for drinking, food production, and various domestic and industrial uses

• It can be a chemical stressor in the aquatic environment, as fluctuating levels of salinity can affect aquatic biological organisms adapted to prevailing salinity concentrations

• Salinity is one of the primary factors used to identify whether a given study site is part of an estuarine or coastal system

Salinity levels in bodies of water can be classified as follows

:

• Fresh water (< 0.05%)
• Brackish water (0.05–3%)
• Saline water (3–5%)
• Brine (> 5% up to 26%–28% max)

In the open ocean, the range of salinity observed is from 33 to 37 practical salinity units (psu)

. Salinity can be measured using a salinometer, which calculates the amount or weight of salt present in a specific volume of water