Saline water is a general term for water that contains a significant concentration of dissolved salts (NaCl). The concentration is usually expressed in parts per million (ppm) of salt.
Water that is saline contains significant amounts (referred to as "concentrations") of dissolved salts. In this case, the concentration is the amount (by weight) of salt in water, as expressed in "parts per million" (ppm). If water has a concentration of 10,000 ppm of dissolved salts, then one percent (10,000 divided by 1,000,000) of the weight of the water comes from dissolved salts.The salinity concentration level used by United States Geological Survey classifies saline water in three categories. Slightly saline water contains around 1,000 to 3,000 ppm. Moderately saline water contains roughly 3,000 to 10,000 ppm. Highly saline water has around 10,000 to 35,000 ppm of salt. Seawater has a salinity of roughly 35,000 ppm, equivalent to 35 g/L.
Some industries make use of saline water, such as mining and thermoelectric-power.
| Water salinity based on dissolved salts in parts per thousand (‰) | |||
|---|---|---|---|
| Fresh water | Brackish water | Saline water | Brine |
| < 0.5 | 0.5 – 30 | 30 – 50 | > 50 |
In the United States, 14 percent of all water used in 2000 was saline.[1] Almost all saline withdrawals, over 92 percent, were used by the thermoelectric-power industry to cool electricity-generating equipment. About three percent of the nation's saline water was used for mining and other industrial purposes.[1]
Due to their proximity to the Atlantic and Pacific Oceans, states near the coast make the most use of saline water. Almost 40% of all saline water use in 2000 occurred in California, Florida, and Maryland.[1]
The use of saline water, as with freshwater, has been trending downward since a peak in 1968. But, in the period between 1950 and 1968, the use of saline water increased at a much higher rate than freshwater use.[1]
The thermal conductivity of seawater is 0.6 W/mK at 25 degC and a salinity of 35 g/kg.[1]. The thermal conductivity decreases with increasing salinity and increases with increasing temperature; these graphs and online calculations plot thermal conductivity for varying salinity and temperature: [2] The salt content can be determined with a salinometer.