What are some drawbacks of desalination at the present?

Answer 1

Cost.

Answer 2

Regardless of the method used, there is always a highly concentrated waste product consisting of everything that was removed from the created "fresh water". These concentrates are classified by the U.S. Environmental Protection Agency as industrial wastes. With coastal facilities, it may be possible to return it to the sea without harm if this concentrate does not exceed the normal ocean salinity gradients to which osmoregulators are accustomed. Reverse osmosis, for instance, may remove 50% or more of the water, doubling the salinity of ocean waste.

The hypersaline brine has the potential to harm ecosystems, especially marine environments in regions with low turbidity and high evaporation that already have elevated salinity. Examples of such locations are the Persian Gulf, the Red Sea and, in particular, coral lagoons of atolls and other tropical islands around the world. Because the brine is more dense than the surrounding sea water due to the higher solute concentration, discharge into water bodies means that the ecosystems on the bed of the water body are most at risk because the brine sinks and remains there long enough to damage the ecosystems. Careful re-introduction attempts to minimize this problem.

The benthic community cannot accommodate such an extreme change and many filter-feeding animals are destroyed when the water is returned to the ocean. This presents an increasing problem further inland, where one needs to avoid ruining existing fresh water supplies such as ponds, rivers and aquifers. As such, proper disposal of "concentrate" needs to be investigated during the design phase.

Answer 3

Contrary to what you sometimes hear, the waste-water from desalination plants is of nearly the same concentration as the water brought in. A small amount of fresh water is removed from a large amount of salt water.

The only problem is the energy consumption that these plants require.

Answer 4

It takes a large amount of energy to desalt sea water. Far, far too much energy to make all our water that way. You might make drinking water that way. You might even make washing water that way. But you could never make irrigation and industrial use water in sufficient quantities that way, It would take more energy than the whole world generates.