The only real problem is the fresh water. The Uk sees to suffer frequent hosepipe bans in hot weather, which the Greenies assure us will become ore so in the future.
So presumably a conflict of use will arise.
No doubt Scotland will be keen on this idea as their objective is to become the leading Green Energy nation on the planet.
I think you may be confusing fresh water with drinking quality water. Fresh water pretty much just means that it has a significantly lower concentration of dissolved salts present in it than seawater. It comes in two types - drinkable and non-drinkable, where the technical definition of drinkable can vary quite widely from one country to another, also known as potable and non-potable (which comes from the Latin word potabilis, which means drinkable). The water subject to hosepipe bans in the UK that is distributed to domestic consumers by water utilities is actually drinking quality water. I don't think I've heard of any water shortages in the UK for non-potable water.
In regard to Scotland being keen on the osmotic power version of renewable energy, I've not heard of that. A quick check of the Wikipedia article "Renewable energy in Scotland" (http://en.wikipedia.org/wiki/Renewable_energy_in_Scotland) suggests they don't currently recognise osmotic power at all, and the article talks up wave power, the UK's favoured method for getting energy out of seawater. The 'strike price' for wave power in the UK is currently £305/MWh (50 cents/kWh), about three times higher than onshore wind and about twice as high as offshore wind.
My view of the Scottish enthusiasm for renewable energy is that this could all change if Scotland votes for independence next year, which I regard as a more likely possibility than most people seem to do. It is very helpful to the Scottish Nationalist cause for renewable energy to be hyped up as much as possible, to bluff the Scottish public into thinking they have some sort of golden future as a renewable energy powerhouse country, as this might further encourage the public into voting for independence. The poor economics of renewable energy will not currently be of much concern to the Scots Nats as the bill is largely being footed by the English, so it's mainly English money that is being wasted, not Scottish money. I suspect that if Scotland became independent, they would scale back the renewable energy ambitions substantially.