Flushing and disinfecting a new cold water system

A new cold water system can carry swarf, jointing debris, dust and contamination from installation, so it is cleaned before anyone drinks from it. Use this checklist to revise the idea; follow the current guidance for the disinfection method and any sampling.

1. Keep it clean as you build. Cap open pipe ends, keep fittings clean and store pipe so dirt and vermin cannot get in, because prevention reduces the cleaning needed later.
2. Flush thoroughly. Once the system is complete and sound, flush it with clean water to carry away debris, working through the outlets so every part of the pipework is cleared.
3. Decide if disinfection is needed. Depending on the type and size of the installation and the guidance that applies, the system may need disinfecting as well as flushing, particularly for larger or stored-water systems.
4. Disinfect properly where it is needed. Use the right method, and keep the disinfectant in contact with the wetted surfaces for the time the procedure sets.
5. Rinse and return to use. Thoroughly flush out any disinfectant afterwards so the water is wholesome before the system is used.
6. Protect stored water. Make sure cisterns are covered, screened and clean so the system stays hygienic after commissioning.

New copper pipework also needs to be used. Normal daily use lays down a protective layer inside new copper pipe. If the pipework is filled, tested and then left standing, especially in a soft water area, that layer cannot form: copper dissolves into the still water, which can run blue, and that is hard to clear once it starts. If new copper pipework will not be used within a few days of testing, drain it down; if you cannot, flush it once or twice a week until the building is in use.

The aim is wholesome water at the tap from day one. Check when disinfection is needed, the method and any sampling against the current Water Regs UK and industry guidance.

Testing before first use

Schedule 2 of the Water Fittings Regulations sets the order in paragraph 13: every water system is tested, flushed and, where necessary, disinfected before it is first used. Testing and flushing always happen; disinfection depends on the installation, and Water Regs UK points to BS EN 806-4 for the method.

Paragraph 12 sets the test pressure at no less than 1½ times the maximum pressure the installation is designed to see in operation. A system designed for a maximum of 4 bar, for example, is tested at 6 bar or more.

• No plastic pipe in the system: pump it to the test pressure, then leave it for one hour without further pumping. It passes if the pressure holds for the hour and nothing visibly leaks.
• Plastic pipe included, Test A: pump at the test pressure for 30 minutes, then reduce the pressure to one third of the test pressure. It passes if the pressure stays at or above that third for the following 90 minutes without further pumping, with no visible leakage.
• Plastic pipe included, Test B: pump at the test pressure for 30 minutes, note the pressure, then stop pumping. It passes if the drop is less than 0.6 bar after the following 30 minutes, or less than 0.8 bar after the following 150 minutes, with no visible leakage.

When a system is also disinfected

After testing and flushing, the guidance to the regulations lists when a system should be disinfected as well:

• a new installation, or a major extension or alteration, except in a private dwelling occupied by a single family;
• underground pipework, except localised repairs or the insertion of junctions;
• wherever contamination may have occurred, such as fouling by sewage, drainage or animals, or entry by people inspecting, painting or repairing it;
• a system that has not been in regular use and has not been regularly flushed.

So new pipework in a family home is tested and flushed, while the same work in a school or a hotel is disinfected as well.