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020 4532 7773If you're connecting a new water system, extending pipework, or bringing a building back into use, you may be asked for a chlorination certificate before the water can be used. It's a common requirement — and one that catches many property owners and contractors off guard. This guide explains what a chlorination certificate is, when you need one, and how the process works.
A chlorination certificate is a document confirming that a water system has been disinfected to recognised standards and is safe to use. It is issued after a competent contractor chlorinates (disinfects) the pipework or storage system and, in most cases, after a water sample has been laboratory-tested to confirm the water is free from harmful bacteria.
Disinfection of new and modified water systems in the UK is typically carried out in line with BS EN 806-4 and BS 8558 — the standards covering the installation and disinfection of water systems intended for human consumption. The certificate records what was disinfected, the method used, and the results of any bacteriological analysis.
You'll usually need a chlorination certificate in any of the following situations:
The underlying legal driver is the Water Supply (Water Fittings) Regulations 1999, which require that water systems do not contaminate the public supply, alongside the general duty to provide safe water.
Chlorination is more than simply adding chlorine. A proper disinfection follows a controlled process:
Because the process must be carried out correctly to be valid — and to avoid damaging the system or leaving residual chlorine — it should always be handled by a competent water treatment contractor.
A good chlorination certificate should record the address and system disinfected, the date, the disinfection method and standard followed, the contractor's details, and — where sampling was carried out — the laboratory results. Keep it on file: you may need to produce it for building control, your water supplier, an insurer, or a compliance audit.
London Water Treatment provides chlorination and disinfection services across London, including new-system chlorination, mains chlorination and remedial disinfection with UKAS water sampling. If you have been asked for a chlorination certificate — or you are commissioning a new system and want to get compliance right first time — get in touch for a quote.
A chlorination certificate confirms a system was clean and safe at the point it was disinfected and tested — it is not an open-ended guarantee. Water quality can change over time, especially if a system is altered, left unused, or poorly maintained. Any new work that opens up the pipework will normally require fresh disinfection and a new certificate, and ongoing water safety is managed separately through routine monitoring and, where needed, a Legionella risk assessment.
The two usually go together but are not the same thing. Chlorination is the disinfection of the system; water sampling is the laboratory test that proves it worked. A thorough certificate is normally backed by a satisfactory water sample analysed at a UKAS-accredited laboratory — so when you commission chlorination, always check whether sampling and results are included.
A competent water treatment or plumbing contractor who has carried out the disinfection to the relevant standards. It should not be self-certified by someone without the right training and equipment.
Certificates are most common for commercial systems, new mains connections and larger installations, but they can also apply to domestic work — for example, a new supply pipe or a stored-water system. If in doubt, check with your water supplier or a water treatment specialist.
