Question

what percent of freshwater can humans use? why?

Answer 1

While nearly 70 percent of the world is covered by water, only 2.5 percent of it is fresh. The rest is saline and ocean-based. Even then, just 1 percent of our freshwater is easily accessible, with much of it trapped in glaciers and snowfields.

http://www.globalchange.umich.edu/globalchange2/current/lectures/freshwater_supply/freshwater.html