Understanding your water pressure system

Help make the best choice when selecting a new tap

Understanding the water pressure system that’s installed in your home is important when choosing taps, showers and other plumbing fittings for your home. Match the right tap or shower to your water pressure and you’ll get great performance – mismatch them and you may find that your taps run very slowly, or hot and cold water runs at different flow rates making it hard to strike a comfortable balance.

Water pressure systems are made up of a combination of a boiler (also known as a combi boiler) and water storage tanks. Some homes may not have a boiler (the water will be heated by electrical elements in a tank or other heater) but will have hot and / or cold water tanks, and others will have a boiler but no water tanks.

There are three main types of system; gravity fed, combi boiler and unvented.

Gravity fed system

These systems are generally found in older properties. You can tell whether you have this system as you’ll have a cold water tank in the loft and a hot water cylinder elsewhere (most likely in an airing cupboard). This means you have a low-pressure water system and you’ll need to choose taps designed to work with lower water pressures.

However, if you have enough height between the bottom of the cold water tank and the tap or shower, it’s possible to have high pressure at that particular outlet, and we’ll show you how to measure this later in the article so you can choose the right taps for your pressure.

A gravity fed system will limit your choice of tap but installing a water pump will increase the pressure and give you access to a wider range of taps and a better shower experience.

Below is an example of an indirect cold water gravity system:

understanding your water pressure system 1

Combi boiler system

If your boiler is wall-mounted and located in your kitchen or hidden away in a cupboard you have a combi boiler system. You won’t have a cold or hot water storage tank meaning you have a high pressure vented water system. This system is an ideal choice for small apartments and new builds as it gives you hot water on demand.

Combi boilers are fed directly with mains pressure cold water, which is then quickly heated and pumped around your home at close to mains pressure. High pressure water systems offer the flexibility of being suitable for use with most taps, so you shouldn’t need to calculate your water pressure when buying new taps.

Pressures can vary depending on your boiler, but the typical pressure expectation is between 1 and 2 bar.

Below is an example of a combi boiler system:

understanding your water pressure system 2

Unvented system

If you have a hot water tank but no cold water tank, you’ll have an unvented water system, providing high pressure.

Water will be stored at mains pressure in a strengthened hot water tank, where it’s heated by immersion heaters attached to the side of the tank or a central heating boiler. It’ll likely be found in an airing cupboard. You’ll have the option to choose from most taps with this set-up, and because it’s high pressure, you shouldn’t need to calculate your water pressure when buying new taps.

With low pressure water systems, it’s important to work out the water pressure to help you buy the correct shower or taps that can work effectively with the pressure you have. The water pressure is measured in bar, and the products designed for this pressure will be labelled accordingly.

To calculate the pressure, you can either ask a plumber to take a look, and they’ll use a pressure gauge tool, which you can also buy and use yourself. Or you can get a rough guide by measuring the drop between the tank and tap.

Start by measuring the height between the bottom of your open or vented water tank and the outlet of your tap. You might find that this means measuring from your tap to your ceiling, and then from the floor of your loft to the bottom of the tank. If there are floors in between, measure the height from floor to ceiling and add this all together. Don’t forget to allow for the depth of each floor too. Try to measure as accurately as possible, to the nearest metre.

Each metre of drop equates to 0.1 bar of pressure (see table below). Water systems which operate at 1.0 bar pressure (10 m of drop) or greater are considered high pressure systems. Those with a pressure less than 1.0 bar are considered low pressure.

Distance Water pressure
1 metre 0.1 bar = Low pressure
2 metres 0.2 bar = Low pressure
3 metres 0.3 bar = Low pressure
4 metres 0.4 bar = Low pressure
5 metres 0.5 bar = Low pressure
6 metres 0.6 bar = Low pressure
7 metres 0.7 bar = Low pressure
8 metres 0.8 bar = Low pressure
9 metres 0.9 bar = Low pressure
10 metres + 1.0 bar = High pressure

When you’re ready to choose a tap or shower, you’ll find the water pressure it’s suitable for will be clearly labelled. Matching the right products to your pressure will ensure they work well in your home.

You can also make changes to your plumbing to increase your water pressure, for example by ensuring your stop valve is open (but not fully).

understanding your water pressure system 3

If you have low water pressure, look for kitchen taps that are labelled as suitable for high and low water pressure systems. Check that the minimum water pressure is the same as, or lower than your water pressure.

If you have high water pressure, you can choose from taps which are labelled as suitable for high and low water pressure systems, or high pressure only.

understanding your water pressure system 4

A low pressure system offers a good choice of showers. Mixer showers (with or without a pump), digital showers (with a pump), electric and power showers will all be suitable as long as the pressure requirement is achieved.

If you have high pressure (achieved with or without a pump), you will get a better flow rate and can consider big rain heads, body jets and the ability to have two or more taps or showers on at the same time.

A high pressure system will work well with a mixer, electric or digital shower. There is no need to install a pump as the water pressure should already be strong.

Pump it up

Adding a pump will help to boost low water pressure systems to give a better performance, but make sure you choose the right pump.

Positive pumps are designed to be fed by gravity. They require a distance of at least a metre between the bottom of the cold water tank and the pump to work.

Universal pumps (also known as negative pumps) do not require a gravity flow of water to function. They are suitable if the showerhead is either level with or above the cold-water tank, for example in a loft conversion.

You can also choose from a twin impeller pump or a single impeller pump. A twin impeller pump is designed for installation into both hot and cold-water supplies, boosting them equally. Single impeller on the other hand can only be installed into a single water supply – either hot or cold.

1.0 bar shower pump 2.0 bar shower pump 3.0 bar shower pump
Boost a single outlet, for example a shower or tap. For boosting increased demand ie large shower heads. For multiple outlets. For multiple outlets. Entire house applications. For large shower heads.

When selecting a pump, consider where it is being located. Pumps will work more efficiently when pushing water rather than pulling water. If possible, your pump should be installed on the floor next to the hot water cylinder and don’t forget accessibility to the pump for future repairs.