Page - 2 - in Water, Energy, and Environment - A Primer

essential ingredients of sustainable economic development. However, there is one critical difference between the two:while energy can be derived from a variety of resources, there is no substitute forwater. TheArab saying ‘water is life’ is a truism– withoutwater youdie. Given the large amount of water on Earth, which has been constant for at least hundreds of millions of years, why are people concerned about water supply? The biggest problem is that most of that water, approximately 97%, is found in the oceans (seawater), with an average salt concentration of 35,000 parts per million (ppm). People and animals cannot drink that water for any length of time without dehydrating internally – the body extracts water from its cells to dilute the ingested salt – and eventually dying from organ failure. Salty (saline) water, such as that found in the oceans, must be desalted (desalinated) to a level at or below 1000ppm for human and animal consumption. Saline water can also impose limits on agricultural production. Oftheremaining3–4%ofwaterontheEarth that is fresh,most is not easily available for our use. Over two-thirds is tied up in glaciers, polar ice caps, and permanent snow cover in mountainous regions, and the rest as groundwater in lakes and rivers, and as water vapor in the atmosphere – and evenmuch of the groundwater is at unreachable locations and depths. The net result is thatwemake productive use of less than 1%of our globalwater resources. 1.2 SALINEWATERANDDESALINATION PROCESSES Salinewater is characterized into three broad categories: • Highly salinewater:more than10,000ppm • Brackishwater: 1000–10,000ppm • Freshwater: less than1000ppm Water,Energy, andEnvironment–APrimer2