<P> The historical focus of sewage treatment was on the conveyance of raw sewage to a natural body of water, e.g. a river or ocean, where it would be diluted and dissipated . Early human habitations were often built next to water sources . Rivers would often serve as a crude form of natural sewage disposal . </P> <P> Over the millennia, technology has dramatically increased the distances across which water can be relocated . Furthermore, treatment processes to purify drinking water and to treat wastewater have been improved . </P> <P> During the Neolithic, humans dug the first permanent water wells, from where vessels could be filled and carried by hand . Wells dug around 6500 BC have been found in the Jezreel Valley . The size of human settlements was largely dependent on nearby available water . </P> <P> A primitive indoor, tree bark lined, two - channel, stone, fresh and wastewater system appears to have featured in the houses of in Skara Brae, from around 3000 BCE, along with a cell - like enclave in a number of houses, that it has been suggested may have functioned as an early indoor toilet . </P>

When was indoor plumbing invented in the united states