Houses built after 1985 in the UK may have a high pressure water system.

The mains water enters the property and flows through a stopcock.
The stopcock can be anywhere but is usually found under the kitchen sink.

Cold water at mains pressure (high pressure) runs to all of the cold cold taps, showers,
toilet cistern and other services. Water also runs through a pipe to a hot water cylinder (tank)
which is usually found in the airing cupboard. The hot water cylinder, which is heated by a boiler,
is made from stainless steel and stores water at mains pressure. Hot water from the cylinder
runs through pipes to all of the hot taps and showers. The hot water cylinder is sealed
and does not have a vent. The hot water cylinder is said to be unvented.

It is called a high pressure system because all of the pipes contain water at a high mains pressure.
The hot and cold water is at the same high pressure and so the system is said to be balanced.
A balanced system is particularly suitable for showers.