Also what is gravity fed? do a lot of properties have a gravity fed system?
Same thing. Pressure comes from tank (cistern) in loft.
History lecture follows:
Unusual (and against current installation regulations) to have cold water to kitchen from stored water (i.e. gravity fed) but very common to have gravity hot water (old-fashioned cylinder) and for many years this was the only way of having hot water in the UK (foreign countries have had unvented cylinders and thermal store boilers for decades but UK regulations deemed this unsafe).
So, if your hot water was low pressure (i.e. gravity fed) and you wanted mixer taps, as they don't work well with high pressure cold and low pressure hot, the cold side of mixer taps in bathrooms also tended to be supplied from the same loft cistern to equalise the pressures. Not a problem if you don't have mixer taps, and some houses have high pressure cold and low pressure hot to all parts of the house. Mine does, for instance.
There is another reason for mains pressure cold, however. Some people (and possibly some local areas when the water Byelaws varied from town to town) preferred not to rely on the mains pressure to feed all the taps at once, so some people preferred a storage cistern for everything but the kitchen sink. A storage cistern has the advantage that if the mains pressure and incoming pipework was not sufficient (especially perhaps in an industrial area where every factory hand arrived at home and wanting a bath at the same time), the storage cisterns could refill slowly as and when mains water pressure allowed.
And even today, there are occasions when perhaps a customer has a large house with lots of bathrooms and mains pressure is not great or the flow rate required for several showers is not available straight off the mains without expensive upgrades, but an old fashioned cylinder with pumped or gravity-fed showers can still work very well.
