Reuters: Following are some facts about strains on the world’s freshwater supplies: OVERVIEW: * Seventy percent of the world’s surface is covered by water but 97.5 percent of that is salt water. Of the remaining 2.5 percent that is freshwater, 68.7 percent is frozen in ice caps and glaciers. Less than one percent is available for human use. * More than 1.2 billion people, about a fifth of humanity, lack access to safe drinking water, according to U.N. data. About 2.6 billion, or …