Does legionella affect drinking water?

Legionella does not infect people through drinking. Legionnaires' disease is contracted by inhaling tiny droplets of contaminated water — the aerosol from showers, spray taps and similar outlets — deep into the lungs. Water that is swallowed takes a completely different path through the body, and that path is not the route by which legionella causes illness. The question is still worth asking, though, because the answer changes how you think about the kitchen tap.

The route of infection: lungs, not stomach

The distinction matters because it directs attention to the right places. The outlets that generate fine, breathable spray — showers above all, plus spray taps, and equipment like hot tubs and cooling towers — are where exposure happens. A glass of water from the kitchen tap does not produce that aerosol in normal use. This is why the guidance concentrates control effort on spray-producing outlets and on the conditions that let the bacteria multiply upstream of them: warmth, stagnation, scale and biofilm. Our page on legionella in water explains where the bacteria actually live in a system.

So why the drinking-water tap is not exempt

Knowing that swallowing is not the route does not make the kitchen tap a free pass. It is still an outlet on the water system, fed by the same pipework as everything else, and subject to the same rules: cold water arriving below 20°C, hot above 50°C, and regular enough use that water does not stand in its branch. More importantly, if sampling ever finds legionella at a drinking-water outlet, the finding is not neutralised by the fact that people drink from it rather than shower under it. A positive result tells you the system has lost control somewhere — the outlet is just where the evidence surfaced — and the response is to investigate the system, following the same logic as what to do if legionella is detected.

Where the contamination actually comes from

Water companies treat and disinfect the public supply, so water crosses the property boundary in good condition. The conditions legionella needs — water held between 20°C and 45°C, standing still, with nutrients from scale and sediment — are created inside buildings: in cold water storage tanks warming in lofts, in calorifiers running too cool at the base, in dead-end pipe runs and taps nobody uses. This is why the legal duty under ACOP L8 falls on the building's duty holder and their water system, and why the practical controls are the building-level ones: temperature, turnover and cleaning, as set out in how to prevent legionella.

What about filters and bottled-water responses?

Where a specific outlet must be protected regardless of system conditions — typically in healthcare, for patients whose immune systems cannot tolerate waterborne organisms — point-of-use filters fitted at the outlet can retain legionella and similar bacteria. They are a targeted clinical measure with their own maintenance schedule, described in our guide to point-of-use water filters, and they are not a general-purpose fix for a poorly controlled system. Likewise, switching a workplace to bottled water after a positive sample does nothing about the showers, the spray taps or the underlying system fault; it addresses the route that was never the problem and leaves the real one untouched.

The practical takeaway for duty holders

Treat every outlet, drinking-water taps included, as part of one system: keep cold below 20°C and hot above 50°C, flush what is little-used, and record it all in the log book. If you are unsure whether your system's temperatures are in range, the temperature checker walks you through the measurement at each outlet. The risk from legionella is real, but it flows through the air from water, not through a glass of it — and the controls follow from that fact.