Well the main ideas are covered here, but one thing you said about lakes and rivers making one sick...
The only make us sick now becasue we dont drink from them. In the past when everyone drank from them, your body was use to the bacteria in it and had no problems with the water.
Personal reference: We moved into a well fed house, whole household got sick. But within a wek we were fine and got to laugh when friends would stay with us and get sick. Just not use to the bacteria in it. Same thing happened to the Conquistidors when the conquered the Aztecs, and what happens to americans visiting Mexico.
So basicaly, we're paying so our body doesn't have to build up immunities and further our physical breakdown as human beings. Oh, and to move it of course...
