A gravity fed, or low pressure, water heating system typically involves a cold water tank in the roof and a hot water cylinder in the airing cupboard. A gravity fed shower receives water under gravity directly from the hot and cold water tanks and mixes them together to reach the desired temperature. The performance of a gravity fed mixer shower is dependent upon having a relatively large hot water tank to supply plentiful heated water, and sufficient pressure to provide a powerful flow of water. If the bottom of your cold water tank is at least one metre above the shower-head then you should have sufficient water pressure for a good flow of water from a gravity fed shower.