What it is
Pseudomonas aeruginosa is a common environmental bacterium that grows readily in moist places and biofilm. It is the organism behind most hot-tub rashes and ear infections, and it is a concern wherever water reaches people whose immunity is reduced.
Where it comes from
It multiplies in warm, standing water: spa pools and hot tubs, hoses, shower heads, tap aerators, water coolers and poorly maintained filters. In a private supply it points to biofilm in tanks or pipework rather than to faecal contamination.
Why it matters
For healthy people the usual effects are skin rash, ear infections and eye irritation after bathing. For people with weakened immunity, wounds or lung conditions it can cause serious infection, which is why healthcare settings and spa pools test for it specifically. The guideline for drinking and pool water is that it should be absent.
What can be done about it
Control is about cleaning, disinfection and keeping water moving: correct disinfectant levels in pools, regular cleaning of filters and surfaces, descaling and disinfecting shower heads and aerators, and removing dead legs. A positive pool result normally means closing the pool, shock dosing, cleaning and retesting.
Information last reviewed 5 October 2026 by Pozzani Pure Water.