Tapping into the Ocean
By Nikolay Voutchkov
Seawater desalination produces fresh, low-salinity potable water from seawater via membrane separation or evaporation. The mineral/salt content of the water is usually measured by the water quality parameter total dissolved solids (TDS), in milligrams per liter (mg/L) or parts per thousand (ppt).
The World Health Organization and the U.S. EPA, under the Safe Drinking Water Act, have established a maximum TDS concentration of 500 mg/L as a potable water standard. This TDS level can be used as a classification limit to define potable water.
Typically, water of TDS concentration higher than 500 mg/L and low or equal to 15,000 mg/L is classified as brackish. Natural water sources such as sea, bay or ocean waters usually have TDS concentration higher than 15,000 mg/L and are generally classified as seawater.
For example, Pacific Ocean seawater along the U.S. West Coast has a TDS concentration of 33,500 mg/L of which approximately 75% is sodium chloride.
Approximately 97.5% of the water on the planet is located in the oceans and therefore is classified as seawater. Of the 2.5% of the planet’s fresh water, approximately 70% is in the form of polar ice and snow, and 30% is groundwater, river and lake water, and air moisture. Even though the volume of the earth’s water is vast, less than 10 million of the 1.4 billion cubic meters of the water on the planet are of low salinity and suitable for use after applying conventional water treatment only. Desalination provides means for tapping the world’s main water resource—the ocean.