The ancient city of Mohenjo-daro (in the Sindh province of Pakistan) had an estimated 700 wells, many of which belonged to private homes. Clean water was in ready supply from underground ...

The cities became overcrowded, with houses built on top of houses. Important buildings like the Great Bath at Mohenjo-Daro were built over. People stopped clearing the drains and they became blocked.

From the carefully constructed streets of Indus Valley to Egypt's lofty pyramids, from the heavens' wisdom of the Maya to the written records of the Sumerians, the earliest civilisations set the stage ...