DROUGHT, NATURAL DISASTERS STILL WHY CAN'T WE CONVERT SEA WATER INTO DRINKING WATER?

Seems strange that water should be such a scarce resource when our planet is drenched in 326 million trillion gallons of the stuff. But it turns out that less than one-half of 1 percent of it is drinkable. Out of the rest, 98 percent is oceanic salt water and 1.5 percent remains locked up in icecaps and glaciers. The stark irony of Samuel Coleridge's immortal line "Water, water, everywhere / Nor any drop to drink" is manifest each year in coastal disasters around the world, like Hurricane Katrina, the 2004 Indonesian tsunami and the 2010 Haiti earthquake, as people within sight of entire oceans are threatened with dehydration.

Between droughts, natural disasters and the large-scale redistribution of moisture threatened by climate change, the need for new sources of potable water grows with each passing day. Each year, the global population swells by another 85 million people, but worldwide demand for freshwater increases at twice the rate of population growth, doubling every 20 years or so. Throughout the world, our most vital resource is under stress from pollution, dam construction, wetland and riparian ecosystem destruction, and depletion of groundwater aquifers, with poor and marginalized populations getting the worst of it

SO WHY CAN'T WE CONVERT SEAWATER INTO DRINKING WATER? 

ANSWER :- 

Actually, we can and we do. In fact, people have been making seawater drinkable at least as far back as the ancient Greeks. But when taken to the scale of cities, states and nations, purifying seawater has historically proven prohibitively expensive, especially when compared to tapping regional and local sources of freshwater. However, as advancing technology continues to drive costs down and freshwater continues to grow scarcer and more expensive, more cities are looking to seawater conversion as a way to meet this vital demand.

There are two process by which we can convert sea water into drinkable water .

1. Desalination

2. Reverse Osmosis (RO)

Both of the process are expensive and lot of energy is lost in these process and get less output. So these process cannot be used. 

How desalination work and something about reverse osmosis.

Desalination has come a long way in the 2,400 years or so since people boiled salt water and collected the steam in sponges. Yet, the most widely used method is still based on the same principle: distillation. Essentially, distillation artificially mimics what occurs in nature: Heated water evaporates to become water vapor, leaving salts and impurities behind, and then condenses as it cools to fall as freshwater (aka rain). Distillation plants refine and speed up this process by applying artificial heating and cooling and by evaporating water under lower air and vapor pressure, which significantly reduces its boiling point. This method requires a great deal of energy, however, so distillation plants are often located alongside power plants, where waste heat is available to bring the water up to a volatile temperature .

Another method, reverse osmosis (RO) desalination, uses pressure to force water through filters, straining out other substances at the molecular level. Developed in the 1960s, the process became feasible on a commercial scale in the 1970s, ultimately replacing distillation as the method used in most new desalination facilities, in part because it requires less energy ]. Besides removing salt, both methods remove virtually every mineral and most biological or organic chemical compounds, producing water that is safe to drink, far exceeding federal and state drinking water standards .