Water Systems - Gravity Fed.

The mains water enters the property and flows through a stopcock before dividing into two pipes.
The stopcock can be anywhere but is usually found under the kitchen sink. One of the pipes
takes water at mains pressure (high pressure) to the cold tap in the kitchen sink. This is the
best tap in the property to drink from. The other pipe runs up into the roof space and fills a large
water tank called the main storage tank (MST) also called the cold water storage cistern (cwsc).
If you have a large tank of water in the loft,
then you probably have a traditional gravity fed low pressure water system.

Water from the main storage tank falls down through pipes which run to the toilet
cistern and cold taps in the bathroom. Tank water also runs through a pipe to a
hot water cylinder which is usually in the airing cupboard. Hot water from the cylinder runs
through the hot water pipes to the hot taps in the bathroom and the hot tap at the kitchen sink.
Another pipe called a vent runs from the hot water cylinder back up into the loft
and over the cold water tank. The vent pipe has an open end. It is a safety feature
and must not be blocked. The hot water cylinder (direct or indirect) is called vented.

The system is called gravity fed because it is only the weight of water falling from the tank
which makes it flow through the pipes. The water is at a much lower pressure than the mains
water (at the kitchen sink) and so a gravity fed system is also called a low pressure system.
The hot and cold water flowing to all the taps (except the kitchen sink - see above) is at the
same low pressure and so the system is said to be balanced. A balanced system is
particularly suitable for showers although the flow rate may need to be boosted by a pump.