---
title: "Saunas and steam rooms: how the Legionella risk differs from showers and spa pools"
source_url: https://legionella.io/articles/sauna-steam-room-legionella/
canonical_url: https://legionella.io/articles/sauna-steam-room-legionella/
pillar: "Building Types & Use Cases"
summary: "A wet steam room's Legionella risk lives in the steam-generator reservoir, not the steam. A dry sauna carries far less; a spa pool, far more. Where to focus."
primary_keyword: "steam room Legionella"
date_published: 2026-05-19
date_reviewed: 2026-06-26
author: "Legionella.io editorial team (REMOTE TECH LTD)"
reviewed_against: "HSE L8 and HSG274 guidance"
region: "United Kingdom"
license: "(c) REMOTE TECH LTD. Quote freely with attribution and a link to source_url."
---

# Saunas and steam rooms: how the Legionella risk differs from showers and spa pools

A wet steam room carries a genuine Legionella risk, and it sits almost entirely in the steam generator's water reservoir and feed — not in the visible steam. A dry sauna carries far less, because it holds no plumbed body of warm water. A spa pool carries the most of the three, and runs under its own rulebook.

Three pieces of kit share the same wet-leisure suite, all run on heat and water, and so they tend to get waved through one risk assessment as if they were the same machine. They are not. Sorting them properly is the difference between maintaining the one that matters and burning effort on the one that mostly does not.

## What actually has to be true for someone to be infected

Legionella makes a person ill by one route: contaminated water broken into a fine aerosol that is breathed deep into the lungs [5]. You do not catch it from swallowing water, and it does not pass between people [5]. The bacteria also need warmth to multiply — broadly the 20–45°C band, with cold water meant to stay below 20°C and hot water kept genuinely hot [2].

So one question sorts these three: does the equipment hold a body of water sitting in that warm band, and does it then turn that water into a breathable aerosol or vapour? Hold that test in mind through what follows.

## The wet steam room: where the risk concentrates

A wet steam room — a Turkish bath or hammam — is filled by a steam generator: a chamber that boils mains or softened water and pipes the steam into the room. The steam at the moment of generation is produced by boiling, which is well above the temperature at which Legionella survives [2]. The visible vapour is, in itself, the least of your worries.

The risk lives in everything around the boil. A steam generator reservoir and its feed sit between sessions, often overnight, cooling out of the boiling chamber and back into the growth band. Scale builds inside the chamber and on the elements, sheltering biofilm. Auto-fill and auto-drain cycles can leave warm water standing. Most overlooked of all is the aroma system many rooms run — a pump injecting a water-based eucalyptus or menthol essence into the steam line, which is a small, room-temperature reservoir with a direct path into the aerosol.

Add the warm, humid room and the condensate running down the walls, and a wet steam room becomes what it is: a system that holds warm water and produces a breathable vapour — the pairing HSE flags as most likely to create a Legionella risk [1]. In character it is closer to the kind of overlooked aerosol source set out in [Misting systems and humidifiers: Legionella in unexpected places](https://legionella.io/articles/misting-systems-and-humidifiers-legionella-in-unexpected-places/) than to a simple hot tap.

## The dry sauna: why the risk drops away

A dry (Finnish) sauna works the opposite way. A stove heats a bank of rocks, the air runs hot and dry, and humidity stays low. Wet vs dry heat is the whole distinction here, and the reason the sauna Legionella risk falls so sharply. A classic dry sauna has no plumbed warm-water reservoir for the bacteria to colonise and nothing that continuously aerosolises water.

The one water source is löyly water — the loyly water ladled onto the hot stones to throw off a brief burst of steam. That pulse lands on rocks far hotter than Legionella can survive, and it is a short burst, not a continuous mist. The sensible precaution is to draw the löyly water fresh and not leave a bucket standing warm for days. The picture only changes if the sauna has been fitted with a plumbed humidifier or an automatic water feed — at which point it stops being a true dry sauna and the steam-room logic applies.

## Sauna, steam room and spa pool side by side

| | Dry sauna | Wet steam room | Spa pool / hot tub |
|---|---|---|---|
| Standing warm-water reservoir | None plumbed; only the löyly bucket | Yes — generator reservoir, feed and aroma dosing | Yes — a large heated body, continuously held |
| Water temperature regime | Hot, dry air; no held water in the growth band | Boiling at the chamber, but reservoir and feed cool into 20–45°C | Held warm, typically in the growth band |
| Aerosol produced | Brief pulse of steam over very hot stones | Continuous breathable vapour | Continuous fine spray from jets and air blowers |
| Relative Legionella risk | Low | Real, and easily missed | Highest of the three |
| Where to put your effort | Keep löyly water fresh; note any plumbed additions | Generator reservoir, descaling, feed temperatures, aroma dosing | Full HSG282 regime |

## The spa pool: a different league, and its own guidance

The spa pool earns the top row for a reason. It holds a large volume of water warmed to around bathing temperature, sat squarely in the growth band, and it aerosolises that water continuously through jets and air blowers while bathers add body fats and organic load that challenge the disinfectant [1][3]. It is the one item here with well-documented outbreaks behind it, which is why it has dedicated guidance of its own. Do not fold a spa pool into a steam-room assessment — run it under [Safe operation of spa pools and hot tubs under HSG282](https://legionella.io/articles/safe-operation-of-spa-pools-and-hot-tubs-under-hsg282/) [3].

## What this means for your assessment

For the steam room, put the generator on a real maintenance schedule: descale to the maker's instructions, manage the reservoir and feed so water is not left standing warm between sessions, keep the feed water within the temperature targets your assessment sets, and treat the aroma dosing line as the small warm reservoir it is [4]. Then handle the rinse and shower facilities around the wet area as the showers they are — the routine for banks of intermittently-used heads is in [Legionella risk in gym and leisure-centre showers](https://legionella.io/articles/legionella-risk-in-gym-and-leisure-centre-showers/).

For the dry sauna, a short, honest entry usually suffices: no plumbed reservoir, löyly water kept fresh, reassess if any water-feed kit is added. For the spa pool, the full regime. The broader spa-and-leisure water safety picture for the whole site is in [Legionella considerations in sports and fitness centres](https://legionella.io/articles/legionella-considerations-in-sports-and-fitness-centres/).

## A fair caveat

This piece explains where the risk concentrates across three common pieces of wet-leisure kit; it is general guidance, not a control scheme for your suite and not legal or design advice. Which items become sentinels, how the steam generator is maintained, what the feed-water targets are, and whether any sampling is warranted are judgements for a competent person working from a current, site-specific risk assessment under ACoP L8 [4][6]. A suite serving older, frail or immunocompromised users carries more weight than a members' gym, and a spa pool always sits under HSG282 in its own right [3].

## Your next step this week

Find the steam generator's manual and answer three things: when was the chamber last descaled, does water sit in the reservoir or feed overnight, and is there an aroma dosing line nobody has cleaned. Those three answers tell you most of what your steam room's risk assessment needs. Then give the sauna its one honest line, and confirm the spa pool is on its own HSG282 regime — three machines, three proportionate responses, instead of one vague entry covering all of them.

## Common questions

### Is the steam from a steam room itself a Legionella risk?

The steam at the point of generation is made by boiling, which is well above the range in which Legionella survives, so the visible vapour is not the main concern [2]. The risk sits in the water that feeds the generator — the reservoir, feed pipework and any aroma dosing solution — which can cool into the growth band and stand warm between sessions, then be carried into the room as vapour [1].

### Does a dry sauna need a Legionella risk assessment?

It should be considered in your site assessment, but a true dry sauna with no plumbed warm-water reservoir is usually a low priority. The main thing to control is the loyly water: draw it fresh and do not leave a bucket standing warm for long periods. If the sauna has a plumbed humidifier or automatic water feed, treat it more like a steam room [4].

### Is a steam room or a spa pool the higher Legionella risk?

Generally the spa pool. It holds a large body of warm water continuously aerosolised by jets and air blowers, with bather load challenging the disinfectant, and it has documented outbreaks and dedicated guidance behind it under HSG282 [1][3]. A wet steam room is a real and easily-missed risk, but a properly maintained one sits below a spa pool.

## Related reading

- [Safe operation of spa pools and hot tubs under HSG282](https://legionella.io/articles/safe-operation-of-spa-pools-and-hot-tubs-under-hsg282/)
- [Legionella risk in gym and leisure-centre showers](https://legionella.io/articles/legionella-risk-in-gym-and-leisure-centre-showers/)
- [Misting systems and humidifiers: Legionella in unexpected places](https://legionella.io/articles/misting-systems-and-humidifiers-legionella-in-unexpected-places/)
- [Legionella considerations in sports and fitness centres](https://legionella.io/articles/legionella-considerations-in-sports-and-fitness-centres/)

## Sources

[1] HSE, "Systems most likely to create legionella risk". https://www.hse.gov.uk/legionnaires/risk-systems.htm
[2] HSE, "Hot and cold water systems". https://www.hse.gov.uk/legionnaires/hot-and-cold.htm
[3] HSE, "Control of legionella and other infectious agents in spa-pool systems (HSG282)". https://www.hse.gov.uk/pubns/books/hsg282.htm
[4] HSE, "Legionnaires' disease. The control of legionella bacteria in water systems - Approved Code of Practice and guidance (L8)". https://www.hse.gov.uk/pubns/books/l8.htm
[5] CDC, "How Legionella Spreads". https://www.cdc.gov/legionella/causes/index.html
[6] HSE, "Legionnaires' disease - what you must do". https://www.hse.gov.uk/legionnaires/what-you-must-do/index.htm