No. Swallowing a glass of tap water, a mouthful from a bottle, or a sip of squash will not give you Legionnaires’ disease. The bacteria that cause it have to reach deep into your lungs, and that does not happen when water goes down your throat into your stomach.
If you are reading this because something worried you, that is the short answer. The longer one is worth a couple of minutes, because the real way Legionella infects people is genuinely different from how most people picture it, and understanding it tells you exactly when there is nothing to fear and the narrow set of situations where ordinary care helps.
The infection comes from breathing in, not drinking down. The bacteria ride on a fine mist of water droplets, small enough to be inhaled, and travel into the lungs [1]. Drinking water bypasses the lungs entirely.
How does Legionnaires’ disease actually spread, then?
Through aerosols. An aerosol is a cloud of tiny water droplets suspended in the air, the kind a shower, a spray tap, or a cooling tower throws off. If that water happens to contain Legionella in high enough numbers, and you breathe the mist in, the bacteria can reach your lungs and start an infection [1].
The droplets have to be tiny to do it. A splash or a stream of water is too big to be inhaled. It is the invisible mist that matters, which is why the highest-risk systems are ones that deliberately or accidentally generate spray: showers left unused for weeks, hot tubs, decorative fountains, and industrial cooling towers [2].
So the route is air, not gut. That single fact explains nearly everything else on this page.
Can swallowing contaminated water make me ill?
Generally, no. Your digestive system is not where Legionella causes pneumonia. The bacteria need lung tissue, and stomach acid is a hostile environment for them. Drinking water that contains the bacteria is not the recognised route of infection [1].
There is one uncommon exception, and it is the source of most of the confusion.
What is aspiration, and is that the same as drinking?
Aspiration is when water “goes down the wrong way” and a small amount slips into the lungs instead of the stomach. It is a recognised but less common route for Legionella to reach the lungs, separate from breathing in a mist [1].
This is not the same as normal drinking. It is the choking-and-spluttering moment, and it mainly matters for people who already have difficulty swallowing safely, such as some older or seriously ill patients in hospital. For a healthy person drinking normally, water goes where it should. Aspiration is why hospitals take their water supplies so seriously, and it is why “you can’t catch it from drinking water” comes with a quiet asterisk rather than being absolute.
Myth vs reality
The gap between what people fear and what actually happens is wide. Here is the honest version.
| What people believe | What actually happens |
|---|---|
| Drinking contaminated tap water gives you Legionnaires’ | Swallowed water goes to the stomach, not the lungs; ingestion is not the infection route [1] |
| Bottled water is “safer” against Legionnaires’ | The risk was never in drinking either way, so bottled water changes nothing about Legionnaires’ |
| Any tap water with bacteria in it is dangerous | Only inhaled aerosols of contaminated water carry the recognised risk [1] |
| You can pass it to your family like a cold | Legionnaires’ disease is not spread by normal person-to-person contact [3] |
| Boiling the kettle leaves you exposed | Boiling kills the bacteria; the brief steam from a kettle is not a known infection source |
The pattern is simple. If water enters your lungs as a breathable mist, there is a route. If it goes down your throat, there is not.
Is my tap water safe to drink?
In the UK, mains drinking water is treated and monitored to a high standard, and Legionella is not a reason to stop drinking from the tap. The concern with the bacteria is about how building water systems are managed, where water sits warm and stagnant and is then sprayed, not about the safety of swallowing a glass of water.
If you want practical reassurance after a property has been empty for a while, run the cold tap for a minute or two before drinking. That flushes through any water that has been standing. It is good housekeeping, not an emergency measure.
What about brushing my teeth or rinsing in the shower?
Brushing your teeth with tap water is not a Legionnaires’ risk. You are not inhaling a fine mist deep into your lungs while you do it.
Showering is the more relevant activity, because a shower head produces exactly the kind of breathable spray the bacteria can travel on. Even then, a well-used shower in a normal home is low risk. The systems that cause concern are ones left unused for long periods, or running lukewarm. If a shower has not been used for a fortnight or more, it is sensible to let it run hot for a few minutes first, with the door shut and yourself out of the room, to clear standing water before you step in.
Can I catch it from someone who has it?
Almost never. Legionnaires’ disease is caught from the environment, from contaminated water aerosols, not from other people [3]. You will not pick it up from a relative’s cough the way you would a cold or flu. Person-to-person spread is not how this disease works in ordinary circumstances.
Who is actually at higher risk?
Most healthy people who breathe in a small number of bacteria will not become ill at all. The disease tends to affect people who are more vulnerable: those over about 45, smokers, heavy drinkers, and people with weakened immune systems or existing lung or chronic conditions [4].
That is reassuring for the worried occupant. It also explains why settings with vulnerable people, such as hospitals and care homes, manage their water far more tightly than an ordinary household needs to.
What should I do if I’m still worried?
If you have flu-like symptoms, a cough, breathlessness, or a high temperature and you are concerned, contact NHS 111 or your GP and mention any exposure you are worried about, such as a hotel stay or a hot tub [4]. Diagnosis and treatment are a clinician’s job, not something to self-assess from a web page.
This article is general information for occupants and members of the public, not a medical opinion about your symptoms or a safety assessment of a specific building. If you live or work somewhere you think the water system is poorly maintained, raise it with whoever is responsible for the premises so a competent person can look at it properly.
The one thing worth doing today: stop worrying about your drinking water, and instead think about anything in your home that sprays water and sits unused, the spare shower, the garden hose left full in the sun, an unused hot tub. Those are where attention actually pays off. If you are the person responsible for a building rather than just an occupant, the same logic is what turns a pile of paper checks into a clear digital record of which outlets get flushed and when.
Sources
[1] CDC, “How Legionella Spreads”. https://www.cdc.gov/legionella/causes/index.html [2] HSE, “Systems most likely to create legionella risk”. https://www.hse.gov.uk/legionnaires/risk-systems.htm [3] CDC, “About Legionnaires’ Disease”. https://www.cdc.gov/legionella/about/index.html [4] NHS, “Legionnaires’ disease”. https://www.nhs.uk/conditions/legionnaires-disease/