Water softeners and filters can protect your plant and improve water quality, but they can also create new places for Legionella and other bacteria to grow if they are not looked after. The main risks are stored water, slow flow and warm temperatures, and the fact that these units are often installed and then forgotten. If you have one, it should be on your Legionella risk assessment and in your maintenance routine.
Why softeners and filters matter for Legionella
Softeners, carbon filters, sediment filters, UV units and point-of-use filters all change the way water moves through a building. Many hold a volume of water, some contain resin or media with a large surface area, and a few sit in warm plant rooms. Water that sits still in warm conditions is one of the things that lets bacteria multiply and form biofilm. Our guide to biofilm in water systems explains why that matters.
Where the risks usually sit
- Standing water in the unit. A softener that is oversized for the building, or a filter on a supply that is rarely used, can hold water for long periods.
- Warm plant rooms. Units installed close to boilers or in poorly ventilated rooms can warm cold water. See our article on plant rooms.
- Filter media and cartridges that are overdue for replacement and have become a surface for bacteria.
- Brine tanks and resin beds that are not cleaned or sanitised as the manufacturer recommends.
- Bypass lines and dead legs left in place after installation, where water does not move.
- Point-of-use filters fitted to taps or showers and left past their replacement date.
Good practice for owners and facilities managers
- Add every unit to your asset register and your Legionella risk assessment, with its location, size and what it serves.
- Follow the manufacturer’s instructions for servicing, regeneration, sanitising and media or cartridge replacement, and keep the records.
- Check the unit is sized for the building. A unit that is too large for current demand holds water for too long, which matters more now that many buildings are used less. See our article on hybrid working and quiet offices.
- Remove redundant pipework and bypasses that are no longer needed.
- Measure temperatures on the cold supply before and after the unit. Cold water should stay cold, and a temperature rise across the unit is worth investigating.
- Record it all in your Legionella logbook.
Does a filter solve the Legionella problem?
Not on its own. A filter is one control among several, and it needs to be maintained for it to work. Some point-of-use filters are used in higher-risk settings to protect vulnerable people, and they are replaced on a schedule. They do not replace temperature control, flushing, cleaning and monitoring. A written scheme should show how each control is managed; see our guide to the written scheme of control.
Where sampling fits
If you are unsure how a softener or filter is affecting your water, sampling before and after the unit can show what is happening. Our article on Legionella sampling and risk assessment explains how the two work together, and how often sampling is typically carried out.
Your duties
The Safety, Health and Welfare at Work Act 2005 requires employers and those in control of workplaces to manage risks to people from their premises and activities, which includes the water systems. The HPSC National Guidelines for the Control of Legionellosis in Ireland (2009) are the main Irish reference. Water treatment equipment is part of the system, so it belongs in the assessment.
Talk to Safer Solutions
We carry out fire risk assessments, Legionella risk assessments, Legionella sampling, water tank cleaning and fire extinguisher servicing for businesses across Ireland, including Dublin, Cork, Limerick and Galway. Call 086 275 9728, email info@safersolutions.ie or send us a message and we will be happy to talk it through.