I think water systems are gravity fed where it's possible, but pumps are added where gravity alone isn't capable of providing the required pressure.
In the UK at various places water is also pumped out from deep wells, these obviously can't be gravity fed
Here's an outstanding example, not far from me, that I've visited a number of times, including when it's in steam.
PPS Main Page
Beautiful place, but now the water is pumped by a small electric sytem in a small shed