Legionella Risk Assessments in Colindale

Legionella Risk Assessments in Colindale: what is different here

The cold supply in this zone arrives close to 20°C in summer

HSE's guidance asks for incoming and stored cold water below 20°C, and for cold outlets to fall below 20°C within two minutes of running. Affinity Water's 2025 report for the Colindale/Kingsbury zone, which supplied about 90,600 people, recorded water temperatures from 6.2°C to 23°C across 228 samples, with an average of 14.7°C. So in late summer the mains water can arrive with little margin before it even enters the building.

That makes how the cold pipes run inside a block more important here. On the visit we run the cold kitchen tap and record the temperature at two minutes. If it is still above 20°C, we note where the pipe runs and whether it shares space with heating pipes.

Heat networks and warm corridors

Colindale Gardens and the new Grahame Park phases are on heat networks, which means hot pipework running through the corridors, risers and ceiling voids of each block, all day and all year. Cold water pipes that share those spaces can pick up heat. Inside the flat, the cupboard holding the heat interface unit often has the cold main running past it.

The parts of this that sit in the common areas are the freeholder's. If a flat's cold water stays warm after running, our record says so, and you can pass it to the managing agent, whose own water safety arrangements cover the risers and any communal tanks or booster pumps.

How hot water reaches the flat changes the risk

HSE says the risk is lower where hot water is heated instantly rather than stored. Many heat interface units produce hot water on demand through a plate heat exchanger, much like a combi boiler, with little stored water in the flat. All-electric flats more often have an unvented electric cylinder, which HSE expects to store hot water at 60°C, with water reaching at least 50°C at the taps within a minute.

Older homes on and around Grahame Park may still have a cylinder and a cold water tank in the loft, and those tanks need a tight-fitting lid and should be free of debris. We record which type you have, the temperatures we measure, any redundant pipework or rarely used outlets, and the condition of shower heads.

Hard water and shower heads

The same zone report gives total hardness of 333 mg/l, with calcium at 133 mg/l. Scale builds up quickly inside shower heads, mixer cartridges and aerators, and scale gives bacteria somewhere to settle. HSE expects tenants to be told to clean shower heads regularly. In a Colindale flat with a rain shower or a concealed valve, we note the cleaning that is due and whether the head can be removed easily.

Empty flats between Colindale tenancies

With 43.5% of households in Colindale South, the ward that includes Beaufort Park, renting privately, flats change hands often, and a gap between tenancies is when water sits still. HSE's guidance is that outlets on hot and cold systems should be used at least once a week while a property is empty, and that the system should be flushed before a new tenant moves in.

For a longer void, a regular flushing routine or draining down may be needed. If your agent holds the keys between lets, agree who runs the taps and shower each week. We can flush the system and record the temperatures on the day of the assessment, which is useful just before a new tenancy.

No certificate, but keep the record

HSE states that health and safety law does not require landlords to obtain a legionella test certificate, and testing is usually unnecessary in a home. There is no fixed review interval either; the assessment should be looked at again when something changes, such as a new tenant, a long void or new plumbing. A written record is only a statutory requirement for employers with five or more employees.

Barnet's published HMO licence conditions do not set a separate legionella rule that we could find, but the HSE duty applies regardless, so a dated record on file is still the easiest evidence that you have assessed the risk.

Official sources

• HSE: legionella and landlords
• HSE legionella temperatures
• Affinity Water AF057 report, 2025
• Cambridge Network, September 2020: Colindale Gardens heat network
• Max Fordham on Grahame Park
• Census 2021 tenure, Colindale wards (Nomis)

Last reviewed October 2026 by EliteShires Property Services.