With the ever increasing shortage of water in reservoirs, why can't we purify seawater to overcome the problem

Answer 1

The simple answer is that we can. However the problem is that it uses loads and loads of energy. There are two ways of doing it. You can either boil up the water into steam and then recondense it into water. Obviously that's going to use loads of energy, as you can see how expensive it is to boil a kettle. The other way of doing it is something called reverse osmosis. This is when you take a really fine filter and push the water through it. The salt then stays on the other side. This is a lot more efficient than boiling it, but it's still very energy expensive. Considering that the greenhouse effect is a big problem because we're using too much energy already, if started producing water by desalination in one way or another, we'd really be in trouble. There's no such thing energetically as a free lunch and what you're trying to do is take salt water which has a great concentration of minerals in it and separate those minerals into a strong concentration of minerals and a strong concentration of water. In other words, you've got to do work to sort the wheat from the chaff. That work comes at a high price. If we do it, we have to burn a fossil fuel in some way or another. The sun does that almost all the time all around the Earth. The sun is hitting the surface of the ocean, evaporating some water and leaving behind the minerals in the sea. The water forms clouds and then comes to Earth as precipitation. So the sun is desalinating all the time, but then the sun has money to burn.

Answer 2

We can do it with very economical means if we want to....evaporative stills can be created on a huge size as are done in Saudi Arabia and other countries but they have plenty of cheap oil to fuel the process. Solar stills can be built that achieve the same results with free energy from the sun as long as it's a geographic area that receives bountiful sunlight. Fresnel lenses can speed up the process as well....they can focus sunlight and reach temperatures of 3000 degrees. Some designs incorporate metal salts which can retain high temp's from this method for extended periods of boiling water when the sky is cloudy. Transportation of the fresh water and removal of the salt, which corrodes the apparatus, are the two biggest and costliest problems with these methods.....distance from the ocean to the area where the water is needed is a prime factor as well.

Answer 3

It is being done in a few places like the Mid East. In addition to fresh water, there are many useful byproducts you could get. Seawater is a primary source of magnesium for the light metal casting industry. If you own a car less than 20 years old it likely has some magnesium parts in it that came from sea water. The US manufacterers often use magnesium; for instance in the streering column air bag actuators.

Answer 4

There will be too much energy consumption. And with ever increasing oil/ nat gas prices heating salt water is too expensive than to find alternatives such as underground aquifers and rain recollection.

Answer 5

We can. It's a matter of finding the most economical way of doing it. I believe that the science is there - it's a matter, now, of correctly applying it to make a viable method of treatment.