Desalination used to be expensive. In the last 4-5 years ultrafiltration (UF) membrane technology for the pre-treatment process plus double pass reverse osmosis process to produce potable water has resulted in costs dropping to around $500/acre foot, ($0.50/m^3 or 1000 liters).

Completely reasonable for coastal cities, if we could be certain they were needed.

Don't forget solar desal. For example, http://waterfx.co. That would eliminate any pollution.

It probably wouldn't. Desalinization leaves a lot of salty brine to be disposed of.

Put it back in the ocean? That's where it was before anyways. It's not like that would have any impact on the salt concentration of the ocean.

> It's not like that would have any impact on the salt concentration of the ocean.

Ocean-wide, no. Where it's dumped, definitely.

My understanding is that desalination doesn't give you crystalline salt, but rather more salty sea water back. Of course you'd have to be careful where you dumped it as a small bay doesn't mix that well. I don't see why you couldn't pipe it out 1-2 miles from the coast. It should mix quite well.