Most deep water is salt laden in some form or another. It can go from lightly salty to complete saturation. Especially in areas where there is oil and gas production. Salt domes and oil just go hand in hand. I would assume it is due to the fact that most of the material that makes oil in the first place is from the bottom of ancient oceans.

None the less you can not confuse deep water with fresh water because it is anything but. Here again you are talking about fresh water that at it's deepest is going to be around 1000 feet. Most of the drilling I see in Arkansas is around 5,000 - 10,000 feet deep.

Considering the water shortages in some parts of the world I'm currently working with the oil and gas industry to try to convert some of the process water to either recycled frac and flood water, or to non-potable irrigation water on the outside best. There is little or no chance of ever being able to clean it up enough to make drinking water out of it because it is cost prohibitive. However, it is fairly easy to make it usable for industry process water. In areas where there is little or no water available it is conceivable that cleaning it up enough to make irrigation water is a feasibility.