One issue of desalination has to be the cost.
Firstly, there is the high installation cost - salty water is very corrosive and the volume of circulating water in the plant is high.
Secondly, it requires a ton of energy to operate. There is the energy needed for water extraction, delivering it to the plant, purification, distributing it and managing discharge. Primarily the purification process is very energy costly because the links between salt and water molecules are very strong.
Furthermore, one has to consider the environmental impact of desalination; it needs a lot of energy resulting in a bigger ecological footprint. However, currently more and more desalination plants connect there receiving energy sources to renewable ones.
Additionally, there are two more environmental complications:
There is the byproduct of super salty water which exists due to the purification process. Little rise in salt content at the outlet of the plant results in the death of most sea life. Next, there is the fact that plankton, plants and small animals get killed at the water intake. Nevertheless, today there are more and more desalinations plants.
For the reverse osmose process, which is the cheapest at the moment, research is developing new membranes with nanotechnology with the material graphene. Also, scientists and companies are developing new technologies like the forward osmosis and dilution solution to name a few.
Are we to depended on ground water? Will there be a water tax in the future in coastal cities which use desalination to cover the cost of the purification process? At what point will it be more cost efficient considering renewable energies?