Water Systems - Gravity Fed.

The most common type of water system in the UK
is a low pressure system called 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.
If you have a large tank full of water in the loft, then you have a traditional
gravity fed system. Water from this tank falls down through pipes which run
to the cold taps in the bathroom and the toilet cistern. Water also runs from the
tank through a pipe to a hot water cylinder which is usually in the airing cupboard.
Hot water from the cylinder runs through more 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 has an open end over the cold tank.
This pipe is a safety feature. The hot water cylinder is said to be 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)
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.

The advantages of a gravity fed low pressure system are
1. There is a tank of stored cold water which you can use if the mains
water stops running due to maintenance or a fault (but see below).
2. The system is balanced which is suitable for showers.
2. A pump can be used to increase the flow rate.

The disadvantages of a gravity fed low pressure system are
1. There is a tank of stored cold water in the loft which may limit the use of space.
2. The flow rate without a pump is often too low for showers.

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