The Romans did not invent it. They were the
first to construct aqueducts the way we know them: a line of arches joined together, with a channel on the top to carry water. They
preferred water from a source (springs) and high up pipes/conduits. Their reasons:
* the water of the Tiber, the river that flows through Rome, was
too dirty to be used as drinking water. The Romans invented the best drains in the world. They
had underground drains to
take away dirty water and sewage. They were flushed
through with water from the baths so that they didn't get too smelly. But ...
this waste water flowed into the Tiber!
* Roman engineers objected against the use of siphons.
conduit high in the air would safeguard the water against
theft and pollution.
Click for more information on When?, Mesopotamia and Greece.