ABSTRACT
For as long as humans have lived together in settlements, they have had an impact on their environment. Trees are cut down to make room for houses, roads are built, and wells are dug or streams are diverted to provide drinking-water. By far the biggest impact, however, is caused by human waste disposal. The larger and more dense the settlement, the bigger and more concentrated the problem. With the development of flush toilets, things really got out of hand.
