Legionella risk assessment in London

Updated 16 August 2026

London has the densest concentration of legionella-relevant premises in the UK: tens of thousands of hotels, care homes, offices, hospitals, and leisure facilities are compressed into a relatively small area served by a mature and ageing water infrastructure. The mix of Victorian plumbing, converted warehouse developments, and modern high-rise residential makes for an unusual variety of water system designs, and London assessors frequently deal with calorifiers older than the buildings that currently host them. Cooling towers serving the capital's commercial estates are concentrated in the City, Canary Wharf, and Midtown, and the local authority notification register is longer here than anywhere else in the country.

Local water supply

The mains water supplier for London is Thames Water (Thames Water website). The mains supply is treated and controlled by the supplier, so your legionella duties begin where the water enters your premises. Anything downstream of the boundary stop tap (storage tanks, calorifiers, pipework, outlets) is your responsibility.

Water in the London area is classed as Hard to Very hard on the Drinking Water Inspectorate hardness scale (around 260-320 mg/l as CaCO₃), according to MyTapWater water quality data (two agreeing sources - unverified). Harder water lays down scale inside calorifiers, cylinders, and mixing valves, and scale gives legionella a foothold while blunting temperature control, so in hard-water areas descaling and inspection belong in the written scheme of control. Check your supplier's postcode water-quality checker for the figure for your exact supply zone.

Legionnaires' disease: the national picture

UKHSA does not publish a separate surveillance figure for London, so no regional number is shown here. The most recent national figure recorded 472 confirmed cases of legionellosis across England and Wales in 2024 — the England & Wales average context, not a count for this region.

UKHSA states figures explicitly for only a handful of regions; a full region-by-region table is not published, and surveillance counts only laboratory-confirmed, reported cases, so the national total is a floor rather than the true number of infections. The full picture, with the trend since 2017, is on the Legionella Data Index. The absence of a regional figure changes nothing about your own duties: a non-domestic water system in London still needs a risk assessment, a control scheme, and the records to show the scheme is being followed.

Typical cost in London

Legionella risk assessment costs in London depend more on the water system than on the location. A rough guide:

• Small premises, mains-fed only, no storage: £150 to £250
• Typical office or shop with a hot water cylinder: £200 to £400
• Care home, hotel, or school with stored hot and cold water: £400 to £800
• Premises with a cooling tower or evaporative condenser: from £800, often much higher

Cooling towers drive the cost up because they are notifiable to the local authority under the Notification of Cooling Towers and Evaporative Condensers Regulations 1992, and they need quarterly sampling and extensive cleaning. Get a tailored estimate with our cost calculator.

Legionella enforcement in London

Prosecutions for legionella failings are usually brought under the Health and Safety at Work etc. Act 1974, whether by the HSE, a local authority, or (in Scotland) the Crown Office and Procurator Fiscal Service. No case in our tracker is recorded in London itself; the cases below are the most recent recorded elsewhere in London, shown as regional context rather than local history. They are drawn from our legionella enforcement tracker, which records each one against its primary source:

St Christopher's Hospice, 2016 (Healthcare). The Sydenham hospice failed to appoint a competent person to control legionella in its hot and cold water system. A patient died of Legionnaires' disease in August 2012 and an orderly later spent 18 days in a coma. Convicted at Southwark Crown Court in 2016 of breaching HSWA ss.2 and 3; sentenced to a two-year conditional discharge and ordered to pay £25,000 in costs. No fine was imposed. Recorded as a prosecution with a death rather than a fine.

The failings behind these cases are consistent: no suitable risk assessment, no written scheme of control, monitoring not carried out, or records that could not show the controls happened. The full dataset is on the enforcement tracker, and legionella fines and prosecutions explains how the courts approach sentencing.

Find a legionella risk assessor in London

We are building a directory of qualified water hygiene assessors in London and across the UK. In the meantime, look for assessors who:

• Work for a company registered with the Legionella Control Association (the LCA is the main UK trade body for water hygiene)
• Hold a City & Guilds or equivalent qualification in legionella risk assessment
• Can provide references from similar premises in the London area
• Will quote against a clear scope (number of outlets, inclusion of hot and cold surveys, whether sampling is included)

Legionella testing labs covering London

Routine temperature monitoring is done on site, but where your risk assessment or written scheme calls for water sampling, the samples go to a laboratory for culture. None of the UKAS-accredited laboratories in our directory is based in London itself, so the nearest UKAS-accredited labs are listed below — all accept postal samples, and posted sampling is how most premises use them:

• Feedwater Laboratories (UKAS no. 2234), turnaround ~10 days, from £82.68 per sample
• Eurofins Water Hygiene Testing UK Limited (UKAS no. 9658)
• ALS Environmental (ALS Laboratories (UK) Limited) (UKAS no. 1314)

Methods, turnaround times and published prices for the full directory are compared on the legionella testing labs page. Sampling is not a substitute for day-to-day control: a clear result records what was found at that outlet on that day, it never certifies a system as safe, and it sits alongside the routine checks in your written scheme of control, not instead of them.

Building types in London

Different building types have specific legionella considerations. Browse the guides most relevant to London premises:

• Landlords and rental properties
• Offices
• Care homes
• Hotels
• Schools
• Dental practices
• All building types