Brackish water is water that has more salinity than fresh water, but not as much as seawater.
Salinity expresses the saltiness or dissolved salt content of a body of water. Technically, brackish water contains between 500 and 30,000 ppm salt - more often expressed as 0.05 - 3.0%.
The concentration of dissolved salts in water partly determines the conductivity when the salt ionises in solution. Electrical conductivity of a water sample is used as an indicator of how salt-free or impurity-free the sample is: the purer the water, the lower the conductivity.
Water salinity based on dissolved salts
< 500 ppm
0.05 - 3.0%
500 - 30,000 ppm
3.0 - 5.0%
30,000 - 50,000 ppm
> 50,000 ppm