We have been talking about sustainability recently, and one of the resources in most jeopardy is fresh water. In the United States the freshwater problem is becoming more and more significant, and in many parts of the world it is already desperate. We shall look at some of the methods used to purify nonpotable water tonight.
First of all, we need to understand what kind of water we are purifying. It ranges in quality from surface or ground freshwater, requiring only minor treatment to eliminate microbes that might cause disease (the vast majority of drinking and industrial water in the United States comes from these sources), all the way to seawater, with lots of intermediate kinds.