Biofilm is a thin, slimy layer of bacteria and other organisms that builds up on the inside surfaces of pipes, tanks, showerheads and other parts of a water system. It matters for legionella control because it gives bacteria somewhere to shelter, feed and multiply, and it can protect them from heat and disinfection. Controlling biofilm is a big part of keeping legionella risk low.
How biofilm forms
Almost any surface in contact with water can develop biofilm over time. It grows fastest where:
- Water sits still, such as in dead legs and little-used outlets.
- Temperatures are lukewarm, in the range where bacteria grow well.
- There is sediment, scale or corrosion for it to cling to.
- Nutrients are present, from debris, rubber washers, certain hoses and fittings.
Why legionella and biofilm go together
Legionella bacteria can live inside biofilm and inside the tiny organisms that graze on it. Bits of biofilm can break away and be carried to outlets. When water is then released as a spray, for example from a shower, the bacteria can become airborne. Breathing in contaminated water droplets is how people catch Legionnaires’ disease. Our post on what Legionnaires’ disease is explains more.
Where biofilm is commonly found
- Showerheads and hoses. See our guide to cleaning and descaling shower heads.
- Cold water storage tanks, especially where there is sediment.
- Hot water cylinders with sludge at the base.
- Dead legs and rarely used pipework.
- Flexible hoses, tap aerators and point-of-use filters.
How to keep biofilm under control
- Keep water moving. Regular use and flushing of little-used outlets, often weekly as typical practice, helps stop water stagnating.
- Keep temperatures right. Hot water hot and cold water cold. Our post on water temperatures for legionella control sets out the principles.
- Clean and descale. Routine cleaning of showerheads, tap outlets and tanks removes the surfaces biofilm grows on.
- Remove dead legs where they serve no purpose.
- Choose suitable materials when replacing fittings, as some rubbers and plastics support bacterial growth more than others. Ask your plumber.
- Get a legionella risk assessment to identify where biofilm is likely in your system.
Sampling and biofilm
A clear sample result is reassuring, but it is a snapshot. Biofilm can release bacteria intermittently, which is one reason sampling supports, rather than replaces, good day-to-day control. See legionella sampling vs risk assessment.
Your duties
Section 19 of the Safety, Health and Welfare at Work Act 2005 requires employers to identify hazards and assess risks, and the HPSC National Guidelines for the Control of Legionellosis in Ireland (2009) give practical guidance on managing water systems.
Talk to us
Safer Solutions provides legionella risk assessments and sampling, with samples analysed by an independent accredited laboratory. Call 086 275 9728, email info@safersolutions.ie or contact us online.
Cold water storage tanks are part of the picture too. Find out about our water tank cleaning and disinfection service, or call 086 275 9728.