Water

Pipe materials

Pipes must not contaminate water, and must be suitable for the pressure, flow and temperature of the water they are carrying.

On this page:

• what to consider
• copper
• polybutylene (PB)
• unplasticised polyvinylchloride (uPVC or PVC-U)
• polyethylene (PE)
• polypropylene (PP-3 or PP Type 3)
• cross-linked polyethylene (PEX)

All of these are acceptable materials for water supply pipes.

Also see:

• hot water pipes for requirements specific to hot water pipes
• pipework jointing systems for details of jointing systems suitable for each type of pipe material.

What to consider

Pipe materials and components must not contaminate potable water. They must also be:

• suitable for the expected temperatures and pressures
• compatible with the water supply, to minimise the potential for electrolytic corrosion
• suitable for the ground conditions (if used underground) to minimise the potential for corrosion of the exterior of the pipe
• suitable for the local climate (if used outdoors) such as freezing conditions or atmospheric salt or sulphur
• able to withstand UV effects (if used outdoors).

So, when selecting of materials for water supply pipes, consider water pressure, water temperature, compatibility with water supply, durability, support, ease of installation, and cost.

Also take account of sustainability considerations such as embodied energy. See material use for more.

Copper

Copper has long been used for all types of domestic water services and distribution because it:

• is durable
• has good corrosion resistance
• is malleable and easy to bend
• is self-supporting
• has good flow characteristics
• requires few fittings
• can be recycled.

Copper may be annealed (i.e. heated, then cooled slowly) which improves its properties, for example making it less brittle and stronger.

Although copper in general has good corrosion resistance, this depends on the environment. Acidic conditions, either from the soil (if buried) or from the water, can cause corrosion, so local pH levels should be checked before using copper pipes.

The use of copper pipes for drinking water supply is somewhat controversial. While copper is an essential trace element, high doses of copper (above 50 mg/kg body weight) can be lethal. The concentration of copper in tap water may increase if low pH water remains in contact with copper pipes and fittings. BRANZ therefore recommends the following:

• Flush the system by running the water for 2–3 minutes or until the water becomes as cold as it will get, if a tap has not been used for approximately 6 hours or longer
• Flush each tap individually before using the water for drinking or cooking
• Do not use water from hot water taps for cooking or drinking, as hot water dissolves copper more readily than cold water does
• The flushed water can be used for washing or for watering plants.

Polybutylene (PB)

Polybutylene is a plastic material that was introduced in the late 1970s and used extensively for water supply pipes until the mid 1990s. Unfortunately, one brand of polybutylene gained a reputation for failure, resulting in a significant drop in use.

Polybutylene has excellent properties for use as water supply pipework, including:

• low cost
• flexibility
• ease of installation
• ability to be used for both hot and cold water services
• frost resistance.

In outdoor situations, it must be protected from UV exposure.

Unplasticised polyvinylchloride (PVC-U or uPVC)

PVC-U is the most widely used plastic piping for water supply pipes and drainage pipes. It can be used in internal, exposed outdoor and underground situations as it:

• is durable
• is inexpensive
• has good flow characteristics
• has chemical resistance
• can withstand UV
• is easy to handle.

It is suitable for cold water services and can be used for limited hot water services as it has a maximum temperature use of 60°C (140°F).

Chlorinated polyvinyl chloride (CPVC or PVCc) is produced by the chlorination of PVC. The result is a PVC pipe with a service temperature of 90°C (190°F) that may be used for hot water supply pipes.

Polyethylene (PE or HDPE)

High density polyethylene (often called alkathene or polythene) has been used since the early 1960s. It is suitable for both potable water and wastewater services but it can only be used for cold water supply.

It is the most commonly used plastic pipe for supplying the mains water to a dwelling. Polyethylene:

• is durable
• is corrosion resistant
• has good flow characteristics
• is lightweight and flexible
• is easy to install
• has a good bending radius
• is inexpensive
• requires few fittings.

Polypropylene (PP)

There are three types of polypropylene:

• P-H has good mechanical properties and excellent chemical resistance for use as industrial and sewerage waste pipes systems
• PP-R has good resistance to high internal pressure so it is suitable for domestic pressure water supply systems and both hot and cold water services
• PP-B is suitable for buried sewerage and wastewater drainage as it has good impact strength, particularly at low temperatures, and excellent chemical resistance.

The use of polypropylene has been increasing since the late 90s as it is:

• chemical and corrosion resistant
• heat resistant
• lightweight
• easy to install
• frost resistant.

In outdoor situations, it must be protected from UV exposure.

Cross-linked polyethylene (PEX)

PEX tubing is made from a cross-linked, high density polyethylene polymer, which results in a stronger material that polyethylene. Properties include:

• more durability under extremes of temperature and chemical attack
• greater resistance to cold temperatures, cracking and brittleness on impact
• it can be used for hot water supply and hydronic heating systems, as well as potable water supplies
• flexibility
• ease of installation
• it can be used for indoor and buried outdoor situations.

PEX is not recommended for outdoor above ground use – although it can withstand some UV exposure, this should not exceed the manufacturer’s instructions.