Legionella Risk Assessments in Northolt

Legionella Risk Assessments in Northolt: what is different here

What Affinity Water's 2025 figures say about the supply

Northolt is in Affinity Water's Greenford/Northolt supply zone, which served 54,924 people in 2025. Across 131 samples that year, the water temperature ranged from 5.2°C to 24.3°C, averaging 15°C, and the residual chlorine averaged 0.59 mg/l. Legionella bacteria multiply mainly between about 20°C and 45°C, so in a warm summer the incoming cold can reach the low end of that range before it has even entered the house.

That makes the cold side worth checking as well as the hot: cold pipes run beside heating pipes, and a loft tank under a hot roof, can warm further.

Loft tanks and cylinders in the interwar semis

An interwar Northolt semi that still has its cold water tank in the loft and a cylinder in the airing cupboard is the typical medium-risk case. The assessment looks at the tank lid, insulation and any debris, the cylinder thermostat setting, and the pipe runs left behind when a bathroom was moved or a combi was added.

Where a combi has replaced the old system but the tank and some pipework were left connected, those dead legs are often the main finding. Removing them is a plumbing job we can quote for.

Hard water, scale and showers

The same Affinity Water report measured total hardness at 305 mg/l and calcium at 122 mg/l. Scale builds up quickly in Northolt shower heads, hoses and thermostatic mixers, and the HSE's guidance for landlords includes cleaning and disinfecting showerheads as one of the simple controls.

Most assessments here therefore recommend descaling shower heads periodically, running any shower that is rarely used, and keeping the cylinder hot enough. That is advice a tenant can follow, so it goes in writing for them as well as for you.

Ex-council blocks: the communal tank belongs to the council

In a flat bought under the right to buy on one of Northolt's estates, Ealing's handbook makes an individual tank in the flat or in the loft above it the leaseholder's, and a communal tank serving several flats the council's. The council's building safety team handles water and legionella compliance for the parts it owns.

Your assessment covers your flat's system: any tank or cylinder that is yours, the immersion heater, and the outlets. If the flat is fed from a communal tank, we note it so the record shows where your duty stops.

Shared houses and voids

A Northolt HMO has more people, more outlets and often a shower or basin in a room that sits empty between lets, so the risk is higher than in a family flat. Ealing's HMO standards require a constant supply of hot water to every bathroom and sink, which in practice means a cylinder or water heater that must be kept at temperature.

For any Northolt property that stands empty, the HSE's advice is to run outlets at least once a week and flush the system before a new tenant moves in. If the assessment finds a higher risk, the written controls will say who runs what and when.

What you get and when to review it

You get a dated written assessment on the day, listing the system, the risks found and the controls that apply to your property. The HSE sets no fixed review interval, and sampling is not usually needed in a domestic let. Review it if the system changes, if the house becomes an HMO, or after a long void. For a combi-fed flat with no stored water, we will often tell you the risk is low and the record does not need repeating each year.

Official sources

• Affinity Water: water quality report 2025, Greenford/Northolt zone (AF061)
• HSE: Legionella and landlords' responsibilities
• Ealing Council: Homeowners' handbook for council leaseholders, October 2025 (repair responsibilities, fire doors, alterations, letting)
• Ealing Council: HMO Standards, April 2025 (fire doors, alarms, sockets, splashbacks, PAT, certificate table)
• ONS Census 2021 via Nomis: type of central heating, Northolt Mandeville and Northolt West End wards (TS046)

Last reviewed October 2026 by EliteShires Property Services.