Water System Chlorination in London: What It Is and When Your Building Needs It

What chlorination does

Chlorination disinfects the internal surfaces of a water system and the water within it. The system is filled and dosed to a set concentration, the solution is held against the surfaces for a specified contact period, and the system is then flushed until the residual returns to the normal level of the incoming supply.

It is a measured sequence rather than a single dose. The concentration is checked at outlets around the system during the contact period so the far end is treated as well as the dosing point. Pre-flushing clears debris and standing water that would otherwise consume the disinfectant. Post-flushing clears the chlorine so nothing corrosive is left behind. Where sampling is required, samples are taken from agreed points and analysed by a UKAS-accredited laboratory.

When a building needs it

New pipework is the most common trigger. Any newly installed distribution system is disinfected before it is put into service, and the record forms part of handover. A new mains connection follows the same pattern: the supply pipe is disinfected, flushed, sampled and documented before the connection is approved.

Alterations and repairs come next. Extending, rerouting or replacing pipework opens the system up, so the affected section is treated again before use. Any repair that exposes the inside of a pipe, fitting or tank is a contamination route and is handled the same way.

Existing systems call for it after certain events. An unsatisfactory sample leads to chlorination as the usual remedial step before resampling. A building brought back into use after standing empty is treated as suspect before residents or staff return. Care homes, schools, healthcare settings and food premises are commonly asked for current records as a matter of sector practice.

Our chlorination services and certificates page sets out the full service, including mains, new pipework, tank and remedial treatment.

What happens on the day

The treated section is assessed first: size, layout, materials, isolation points, access and the date the paperwork is needed by. On the day, the section is isolated and outlets are identified so water is not drawn during the works.

The system is flushed to clear debris and standing water. Tanks are physically cleaned first where they form part of the treated section. The system is then dosed, held for the contact period with concentrations checked around the network, flushed back to background level, and sampled where required. Samples go to the laboratory and the certificate follows once satisfactory results are received.

Work on site is often completed within a working day depending on the size and complexity of the system. Laboratory turnaround typically decides the overall timetable, so the chlorination should be booked before the connection or handover date rather than after it.

Chlorination, tanks and pipework

Storage tanks and pipework are treated as one system. A tank is drained and cleaned by hand before disinfection, because disinfectant cannot act reliably through sediment or scale. Pipework is flushed before dosing for the same reason. Where a Legionnaires’ assessment has flagged the tank, the pipework or both, the treatment is scoped from those findings.

Where pipework alone is the concern, pipework disinfection covers flushing and disinfection of new, altered or existing pipework. Where tank condition is the concern, water tank cleaning covers inspection, cleaning, disinfection and sampling. Where laboratory confirmation is the main requirement, water testing and sampling covers collection and analysis.

How to prepare for a chlorination visit

Five points make the visit straightforward. Confirm what has been installed or altered and which section needs treating. Note whether there is a cold water storage tank and where it sits. Count roughly how many outlets are involved. Flag access constraints such as locked plant rooms, roof-level tanks or occupied areas. Give the date the certificate is needed by at the time of booking, so sampling can be planned around it.

Need chlorination for your system?

Tell us the property, the system and the date the paperwork is needed by. We are open Monday to Sunday, 8:00am to 6:00pm. Call 020 7101 3229 or email Londonchlorination@gmail.com. For written enquiries, use the contact page or WhatsApp via https://wa.me/447408633324.

Frequently Asked Questions

What is water system chlorination?

The controlled disinfection of a water system with a chlorine-based solution, carried out at a set concentration for a specified contact period, followed by flushing and, where required, laboratory sampling.

When is chlorination required?

Commonly for new pipework, a new mains connection, alterations or repairs that open the system up, an unsatisfactory sample, a building brought back into use, or where current certification has been requested.

Is the water safe to use straight after chlorination?

The system is flushed back to background level before it returns to service, and where sampling is required the results confirm the outcome against the tested indicators. The certificate records that outcome with its date.

How long does chlorination take?

Work on site is often completed within a working day depending on system size and complexity. Laboratory turnaround for samples typically adds a few working days, which is why early booking matters.

Does chlorination include a certificate?

Where certification is required, the certificate is issued following completion, with the laboratory report attached where sampling was carried out. It records the system, date, method, standard and results.

Can chlorination be combined with tank cleaning or testing?

Yes. Tank cleaning, chlorination, pipework disinfection and water testing and sampling are commonly combined into one programme, scoped from the assessment findings or the sample results.