The USGS Water Science School
Care to guess what percentage of Earth's water is saline?
First, what do we mean by "saline water?" Water that is saline contains significant amounts (referred to as "concentrations") of dissolved salts. In this case, the concentration is the amount (by weight) of salt in water, as expressed in "parts per million" (ppm). If water has a concentration of 10,000 ppm of dissolved salts, then one percent (10,000 divided by 1,000,000) of the weight of the water comes from dissolved salts.
Here are our parameters for saline water:
Source: Saline-water resources of North Dakota, USGS Water Supply Paper 1428, 1958.
So, with all of the water available on Earth how come we are worried about water shortages? In a way, it comes down to water-quality considerations rather than water-quantity problems. Slightly saline water is sometimes used for similar purposes as freshwater. For example, in Colorado, water having up to 2,500 ppm of salt is used for irrigating crops. Normally, though, moderate to high saline water has limited uses. After all, you don't drink salt water at home; you don't use it to water your tomatoes or brush your teeth; farmers don't usually irrigate with it; some industries can't use it without damaging their equipment; and, farmer Joe's cows won't usually drink it. So, is saline water good for anything?
There are two answers -- both "yes." Saline water is useful for some water-use purposes, and saline water can be turned into freshwater, for which we have many uses.
You might want to take a look at where is Earth's water located.
The water cycle: Oceans
Uses of saline water Have a cup of seawater Why is the ocean salty?