Water pressure

[edit] Introduction

Water pressure is the continuous physical force that enables water to move through pipes, plumbing and other water distribution systems.

[edit] Related water concepts

Water pressure is not the same as hydrostatic pressure, which refers to: ‘The pressure exerted by water at rest.’ It also differs from hydraulic pressure, which refers to: ‘The pressure exerted by water (whether at rest or moving) on a surface or structure. Hydraulic pressure has the units of force per unit area and is calculated for water at rest as the product of the depth of water and its density. The pressure can differ for water in motion.’ Ref Culvert, screen and outfall manual, (CIRIA C786) published by CIRIA in 2019.

In plumbing terms, water pressure differs from water flow, which is the amount of water that passes through pipes. This amount is determined by the width of the pipes, so narrow pipes tend to have a lower flow than wider pipes. However, higher pressure levels will move water at greater flow rates

[edit] Generating water pressure

Water pressure can be created by the weight of water as the pull of gravity moves it from a higher point to a lower point. This pressure depends on the altitude of the water source (such as a reservoir or water tank). In most cases, a higher location or altitude results in greater water pressure.

Pumps can also be used to control water pressure in certain instances - such as in fire suppression systems or power washing devices - or places where it is necessary to rely on methods other than the natural forces of gravity. In buildings, pressure pumps can be used to increase the movement of water inside the structure (for toilets, taps and other sanitary appliances, heating systems and so on) or for use in landscaping irrigation systems.

[edit] Water pressure problems

Water pressure requirements are dictated by Ofwat, which is the Water Services Regulation Authority for England and Wales. Through the guaranteed standards scheme (GSS) Ofwat offers guidance regarding the level of service customers are entitled to from their water suppliers.

It is the responsibility of water companies to provide acceptable water pressure to customers, since both high and low levels can be the source of problems.

[edit] High pressure

Excessively high water pressure can damage fixtures and cause appliances to wear out sooner than they generally would. It may also create leaks, wear out seals or make pipes burst - resulting in wasted water, flooding and property damage.

High pressure levels are frequently created by third parties such as municipal operators or commercial water suppliers, for example when rerouting water supply networks or as a result of proximity to fire hydrants.

Customers may also experience unanticipated high pressure levels under other conditions created on site, including air trapped in water pipes or faulty expansion tanks on water heaters.

[edit] Low pressure

Customer inconvenience is one of the common consequences of low water pressure. In certain instances, some appliances may not work at all if levels are too low.

If low pressure conditions exist, Ofwat’s GSS states that “A company must maintain a minimum pressure in the communication pipe (the pipe which carries water between the water mains and the boundary of private property) of seven metres static head (0.7 bar). If pressure falls below this on two occasions, each occasion lasting more than one hour, within a 28-day period, the company must automatically make a GSS payment to the customer. There are exceptions to the requirement to make a GSS payment if the pressure standard is not met."

There may be several external causes of low pressure, including:

• High demand when numerous pieces of plumbing equipment (such as taps, showers, dishwashers and so on) are in use at the same time.
• Broken pipes or other emergencies that create unanticipated or uncontrollable usage.
• Dry weather conditions that cause people to resort to using sprinklers or hoses to water gardens.
• Inadequate facilities (such as inefficient pumping stations or small water mains), blocked pipes or other equipment failures.

On the premises, malfunctioning equipment (such as problems with certain types of internal stop taps) and leaks can also result in low water pressure.

[edit] Addressing pressure issues

Providers can address issues by removing corrosion in water mains, replacing the linings, replacing mains, installing pumps, repairing leaks and so on. If water pressure issues persist, customers may find it beneficial to install water meters in order to monitor significant changes in pressure. These meters should not bring about any significant changes in water pressure. Further measures may be required, including reporting issues to the water company or contacting the Consumer Council for Water (CCWater) to register a complaint.

[edit] Related articles on Designing Buildings

• Consumer Council for Water CCWater.
• High pressure water jetting.
• Hydram.
• Hydraulic pressure.
• Hydrostatic pressure.
• Ofwat.
• Plumbing.
• Pumping station.
• Water hammer.
• Water tank.

[edit] External resources

• CIRIA, Culvert, screen and outfall manual (CIRIA C786).
• Consumer Council for Water (CCWater), Make a complaint.
• Ofwat, The guaranteed standards scheme.