Selecting materials for cold water systems

Suitability for wholesome water

Every material in contact with wholesome cold water must be suitable for that duty: it must not contaminate or taint the water, and it must suit the pressure and temperature it will meet. Lead is not acceptable for new pipework carrying wholesome water because it can leach into the supply.

Common choices

• Copper: widely used, durable, suitable for hot and cold.
• Blue MDPE: a usual domestic underground-service choice, subject to product approval, ground conditions and the water undertaker’s requirements.
• Plastics such as PE-X and PB: flexible and quick to install, used for hot and cold within buildings up to their rated limits.
• Stainless steel and suitable fittings where specified.

Practical cautions

• Do not run the blue underground supply pipe through heated areas where its temperature rating would be exceeded; carry the rising main indoors in a suitable material.
• Where the ground may be contaminated, a barrier pipe may be needed so contaminants cannot permeate the supply pipe.
• Avoid arrangements that drive corrosion, such as poorly chosen dissimilar metals in contact.

Choose products suitable for contact with wholesome water and confirm each against manufacturer data, the Water Fittings Regulations and current WaterRegsUK guidance.

Valves, drain-offs and identification

• Each separate premises has its own stopvalve, so its supply can be shut off without affecting anyone else.
• Servicing valves on a cistern's inlet and outlet, and next to appliances and float valves, let one item be isolated and replaced without draining the system.
• A system must be capable of being drained down, with enough servicing valves and drain taps to limit the water lost during maintenance; accessible drain-offs let sections be emptied safely for repairs and alterations.
• A pressure-reducing valve controls excessive inlet pressure within its specified duty. Select it for flow capacity as well as the setting. It can help where excess pressure contributes to noise or waste, but noise and water hammer still need checks on velocity, valve closure and pipe support.
• On larger systems, balancing valves stop the nearest branches taking more than their share of flow and starving remote outlets.
• Clearly identify non-potable pipework and prevent unprotected cross-connections with the wholesome supply. Any permitted top-up or connection must use the appropriate approved backflow arrangement for the fluid category and mechanism; identification is not physical protection.