Saline water is water that contains a high concentration of dissolved salts. The salt concentration is usually expressed in parts per thousand or parts per million (ppm). The United States Geological Survey classifies saline water in three salinity categories. Salt concentration in slightly saline water is around 1,000 to 3,000 ppm (0.1–0.3%), in moderately saline water 3,000 to 10,000 ppm (0.3–1%) and in highly saline water 10,000 to 35,000 ppm (1–3.5%). Seawater has a salinity of roughly 35,000 ppm, equivalent to 35 grams of salt per one liter of water. The saturation level is only nominally dependent on the temperature of the water. At 20 °C one liter of water can dissolve about 357 grams of salt, a concentration of 26.3% w/w. At boiling (100 °C) the amount that can be dissolved in one liter of water increases to about 391 grams, a concentration of 28.1% w/w.
