Yes — a domestic hot tub is a genuine Legionella risk, and not a small one. It holds water at roughly body temperature for weeks, pushes the same water round a filter again and again, and blows it into the air as a fine spray. Warmth, recirculation and aerosol are the three things Legionella needs to breed and then reach your lungs. A garden spa ticks all three at once.

That is not a reason to drain it in a panic. It means a hot tub earns a maintenance routine a cold, fast-emptying paddling pool never does — and if you let your place to guests, it earns rather more than that.

Why a bubbling tub is not just a small swimming pool

People file hot tubs mentally next to swimming pools, and that is where the misjudgement starts. A pool holds a large volume of cooler water, turned over and re-dosed constantly, with a big disinfectant buffer. A hot tub is the opposite on every axis — and a small inflatable or portable spa is more extreme still: a tiny volume of warm water, used by a few people who each add organic matter that eats the sanitiser fast, with very little spare water to dilute anything that goes wrong.

Two of those features are what control people call amplification and exposure. Legionella multiplies most readily in water roughly between 20 and 45°C, and a spa deliberately parks itself in the middle of that band [3]. Then the air jets that make it pleasant whip the surface into a breathable mist — and breathing in contaminated droplets, not swallowing them, is how Legionnaires’ disease is caught [5]. The HSE lists spa and hot tub systems among the systems most likely to create a foreseeable Legionella risk for exactly this reason [1]. A warm tub that has sat unused under its cover, then fires its jets for the first time in a fortnight, is the scenario that worries people who do this for a living. It is the same logic that makes a rarely-run home shower worth attention — see Can you catch Legionnaires’ disease from your home shower? — only a hot tub aerosolises far more water, far closer to your face.

Homeowner or host: the duty is not the same

For a hot tub you own and use yourself, there is no specific Legionella “law” pointed at you. You are managing your own household’s risk, and the routine below is how you do that sensibly.

The picture changes the moment money and guests enter. If your hot tub is provided as part of a business — a holiday cottage, an Airbnb, a glamping pod, a B&B — it is treated as a business-use spa system, and a commercial-style duty applies. That means assessing and controlling the foreseeable risk, and running the tub broadly along the lines the HSE sets out in HSG282 rather than on the casual empty-and-refill habit you might accept at home [2][4]. The dedicated guidance for commercial spa systems is summarised in Safe operation of spa pools and hot tubs under HSG282; the wider short-let obligation is set out in Do you need a Legionella risk assessment for a holiday let or Airbnb?, and operators covered by Legionella control in caravan parks and holiday parks face the same reasoning across multiple units.

The practical sting for hosts is the changeover gap. Between bookings the tub sits warm, covered and still — prime breeding conditions — and then a new family climbs in and turns the jets on. Your control has to bridge that gap, not just the moments when someone is watching.

The routine that keeps a domestic spa safe

Treat upkeep as four habits, not one annual chore. Tick and date them — a host will need that record to show control; a homeowner will simply find the tub stays clearer for it.

Every time, before and after a soak

  • Check the water looks and smells clean before anyone gets in; cloudy, smelly or slimy water means stop and drain, not “add more chemicals”.
  • Test and correct the sanitiser and pH before use with your tub’s strips or kit — bromine or chlorine, held within the range your manual states.
  • Run the jets for a minute or two with nobody leaning over the tub after any quiet spell, ideally with the cover off and good ventilation, so you are not standing in the first burst of aerosol.

Weekly upkeep

  • Keep the disinfectant — the biocide — topped up between soaks; warmth and bathers knock it down quickly, and an undosed tub loses control within days.
  • Remove and rinse the filter cartridge under clean water to clear grease, hair and debris.
  • Wipe the waterline, the cover underside and the headrests, where biofilm and scum gather out of sight.

The full drain, clean and refill

  • Drain the tub completely on the cycle your manufacturer specifies — counted in weeks, and sooner the harder it is used. Do not nurse the same fill for months.
  • With it empty, clean the shell and jets, and flush the plumbing with a proprietary spa-line cleaner to shift the biofilm a wipe alone leaves behind.
  • Deep-clean or replace the filter cartridge; a tired cartridge is a permanent reservoir no amount of dosing fixes.
  • Refill, balance the chemistry and bring it up to temperature before the next use.

Extra steps if guests use it

  • Drain, clean and refill between lets wherever you reasonably can, rather than running guest after guest on one fill.
  • Keep a dated log of every drain, clean, filter change and water test, per property — the evidence that your control is real.
  • Hold a written risk assessment for the tub and follow the HSG282-style regime it sets; do not assume a domestic routine is enough once you are charging for it.

On the chemistry and the numbers

I have kept specific figures out of this deliberately. The right sanitiser, the range to hold it in, the pH window and how often to drain depend on your particular tub, how hard it is used and the product you run — and they belong in the manufacturer’s manual and, for a let, a competent risk assessment, not in a number lifted from an article [2]. Where this guidance and your tub’s manual ever disagree, the manual wins.

And the honest caveat: this is general information, not a survey of your spa or legal advice. A private garden tub, a holiday-cottage tub and a glamping site with several spas are genuinely different risks, and only a competent person working from your actual setup can fix the right measures and frequencies. Nothing here is medical advice either — if you think anyone has become unwell after using a tub, that is a question for a doctor, not a logbook.

FAQ

Can you really catch Legionnaires’ disease from a home hot tub?

The risk is real because the route fits: a hot tub makes a warm, breathable spray, and inhaling contaminated droplets is how the infection takes hold [5]. Most home tubs that are dosed, drained and cleaned on schedule stay safe — the danger sits with neglected water left warm and undertreated, then aerosolised by the jets. Keeping the biocide up and the water fresh is what removes the hazard.

How often should I drain and refill a domestic hot tub?

Follow your manufacturer’s cycle, which is usually counted in weeks and shortens the more people use the tub and the harder it is used. A small spa run hard at a party fouls far faster than one used by a couple at weekends. If the water turns cloudy, smells off, or will not hold its sanitiser, drain it early regardless of the calendar.

Do I need a Legionella risk assessment for a hot tub at my holiday let?

If the tub is part of a let, treat the answer as yes. A hot tub provided to paying guests is a business-use spa system, so you should hold a risk assessment and run it on an HSG282-style regime rather than the relaxed routine you might use privately [2][4]. The detail sits in the holiday-let and HSG282 articles linked above.

What to do next

If your tub has stood unused for more than a few days, do not climb straight in. Lift the cover, check and correct the chemistry, then run the jets for a couple of minutes from a distance with the area ventilated before anyone uses it — and note the date you did it. If you let the property out, turn that into a fixed changeover step and start a dated drain-and-clean log per tub today; an outlet you can prove you maintained is the line between control and luck.

Sources

[1] HSE, “Systems most likely to create legionella risk”. https://www.hse.gov.uk/legionnaires/risk-systems.htm [2] HSE, “Control of legionella and other infectious agents in spa-pool systems (HSG282)”. https://www.hse.gov.uk/pubns/books/hsg282.htm [3] HSE, “Legionnaires’ disease: Technical guidance (HSG274)”. https://www.hse.gov.uk/pubns/books/hsg274.htm [4] HSE, “Legionnaires’ disease - what you must do”. https://www.hse.gov.uk/legionnaires/what-you-must-do/index.htm [5] NHS, “Legionnaires’ disease”. https://www.nhs.uk/conditions/legionnaires-disease/