How to Clean an Ice Bath: Water Changes, Sanitiser and Maintenance

Most ice baths go bad for the same reason: people fill them, plunge happily for a fortnight, then lift the lid one morning to find green water and a film on the walls. Keeping the water clean is far less work than fixing it afterwards, and the routine is simple. Shower before you get in, keep the lid on, change the water on a schedule that matches how you use the tub, and if you want to go longer between changes, add filtration and a sanitiser. The rest of this guide is the detail behind each of those.

How often to change ice bath water

There's no single answer, because it depends on three things: whether the tub has a filter, whether you add a sanitiser, and how many bodies go in it each week. Here's what we'd work to.

Setup	Typical use	Full water change
No filter, no sanitiser	1 person, 3 to 4 plunges a week	Every 3 to 7 days
No filter, sanitiser dosed by hand	1 to 2 people	Every 2 to 4 weeks
Filter pump plus sanitiser	1 to 2 people, daily	Every 4 to 8 weeks
Chiller with filter and ozone or UV plus a residual sanitiser	Daily, household use	Every 1 to 3 months, or as the maker advises

Bigger tubs don't automatically last longer. A 500 litre barrel dilutes contamination more than a 250 litre one, but it also costs more to refill and chill, which tempts people to stretch it. Shared tubs need changing more often than solo ones, and a tub that sits in direct sun warms up and turns faster than one in a shaded garage.

For context, HSE's guidance on spa pools used commercially expects the full volume to be replaced weekly, or after each group of users if sooner (HSE HSG282). That's written for heated hot tubs with heavy bather loads, so it's stricter than a home ice bath needs, but it's a useful ceiling: if you've no filter and no sanitiser, a week is about as far as you should push it.

Daily habits that keep the water clean

These cost nothing and do more than any chemical.

1. Rinse or shower first. Sweat, skin oils, sun cream and deodorant are the food bacteria live on. A 30 second rinse before you get in removes most of it. If you plunge straight after a run, this matters twice as much.
2. Keep the lid on. A lid blocks sunlight (which feeds algae and warms the water), leaves, insects, pollen and bird droppings. Most of the tubs we've covered ship with one; use it every time, not just overnight.
3. Skim it. Pick out leaves, hair and grass with a cheap pool skimmer net before they sink and rot.
4. Don't plunge with open cuts or if you've had a stomach bug in the past 48 hours.
5. Keep it cold. Water held under 15C turns much more slowly than water drifting towards 20C, and our guide to ice bath temperature covers how to get there without overspending on ice.

Filtration and chillers with filters

A filter doesn't disinfect the water, but it strips out the hair, skin flakes and debris that a sanitiser would otherwise be fighting. Cartridge filters on tubs like the Lay-Z-Spa Glacial Dip need rinsing with a hose every week or so and replacing every few months; a clogged cartridge circulates water without cleaning it.

Chiller units usually combine a pump, a filter and sometimes ozone or UV. Ozone and UV are genuinely useful, but HSE is clear that neither works on its own: UV only kills bacteria at the point the water passes the lamp, and ozone must be used alongside a residual disinfectant. Treat them as helpers, not a replacement for sanitiser. If you're weighing up a chiller, our AS ColdPlunge chiller review and the Zennest chiller tub review cover what the filtration actually does on each.

Sanitising options and how much to use

Always follow the dose on the product label for your tub's volume, and buy a pack of spa test strips (around £10 for 50) so you're measuring rather than guessing. The figures below come from HSE's spa pool guidance, which is the most authoritative UK reference available, though it's written for heated commercial tubs.

Hydrogen peroxide

Silver stabilised hydrogen peroxide is the option most cold plunge makers recommend. It breaks down into water and oxygen, doesn't smell, and doesn't need pH adjustment. HSE describes an initial shock dose of 100 ppm for at least 12 hours, then a running residual of about 50 ppm (30 to 70 ppm). Use a product sold for hot tubs; don't pour in high-strength peroxide from a chemist, which can irritate skin and damage liners.

Chlorine or bromine

Spa chlorine granules (dichlor) are cheap and effective in cold water. HSE's target for spa pools is 3 to 5 mg/l free chlorine, or 4 to 6 mg/l bromine, with pH between 7.0 and 7.6. At home, with one person in cold water, sitting at the lower end is plenty, and you'll find the tub needs much less topping up than a hot tub would. Bromine is gentler on the nose but slower to dissolve in cold water; chlorine is the simpler choice for most people.

Ozone and UV

Built into some chillers. Useful for knocking down bacteria as water circulates, but you still need a low residual of chlorine, bromine or peroxide in the tub itself.

What not to use

Household bleach for routine dosing (fine for scrubbing an empty tub, hard to dose accurately in a full one), Epsom salts as a "cleaner" (they aren't), and mixing different sanitisers in the same water.

How to drain and scrub the tub

Plan a deep clean at every full water change.

Inflatable and PVC tubs: drain via the valve with a hose to a drain or flower bed, not across a patio. Once it's empty, wipe the walls and floor with a soft sponge and warm water with a little washing-up liquid, paying attention to the waterline, seams and around the valve. Rinse well and let it air dry for an hour before refilling. Avoid scourers and solvent cleaners, which scuff PVC and give biofilm somewhere to grip. Tubs with a removable liner, like the Replenished 370L, make this a ten minute job.

Rigid tubs and chiller units: drain, scrub the shell with a soft brush, then clean the filter. Every few months, or after any water that went bad, run a line cleaner or a sanitiser flush through the chiller's pipework following the maker's instructions. Pipework is where biofilm hides, and draining the tub doesn't touch it.

Biofilm forms on wet surfaces across a wide range of temperatures, and it grows faster when nutrients from skin and sweat are in the water (Jarząb and Walczak, 2017). That's the case for showering first and for physically scrubbing rather than just refilling.

Signs the water has gone bad

• Slimy walls or a slick feel underfoot: biofilm. Drain and scrub.
• A musty, swampy or eggy smell. Clean water smells of nothing.
• Cloudy or green water, or a visible ring at the waterline.
• Foam that sits on the surface after you get out, usually from body oils and product residue.
• Itchy red bumps after plunging. This is the pattern of "hot tub rash", a Pseudomonas skin infection, which a London case report in the British Journal of General Practice flagged as a risk of the lockdown home hot tub boom (Osborne et al, BJGP 2021). Stop using the tub, drain and disinfect it, and see your GP if it doesn't settle.

Any one of these means change the water today.

Legionella and Pseudomonas: the honest risk

Legionella is the bacterium behind Legionnaires' disease, and HSE notes it grows most readily between 20C and 45C, which is why hot tubs are a recognised source. Two things put most ice baths in a better position: the water sits well below 20C, and most plunge tubs don't have jets that throw a fine spray you'd breathe in.

That's lower risk, not zero risk. An unchilled tub in a sunny garden in August can reach the high teens or low 20s. Chillers have pumps and pipework where water sits warmer and still between sessions. And Pseudomonas, which causes skin and ear infections rather than pneumonia, doesn't need hot water to survive. Keep a sanitiser in the water, keep it cold, and don't leave a tub full and untouched for weeks, then start using it again without a change.

Winter and storage

Winter is the easiest season: mains water arrives cold, algae barely grow, and the water lasts longer. The risk is frost. A full PVC tub generally copes with a light freeze, but a long hard frost stresses seams, and chillers or plastic valves can crack if water freezes inside them. If a prolonged freeze is forecast and you aren't plunging, drain it.

To store a tub, drain it completely, clean and rinse it, then let it dry fully, inside the hoses and fittings too, before folding. HSE's guidance for spa pools is the same: store them dry, pipework included, as far as practicable. A tub folded damp grows mould in a cupboard within weeks. Before the first plunge of the new season, give it a full clean and a fresh fill.

Recommended reads

• Best ice bath UK: the tubs we rate, including options with filters and chillers
• What temperature should an ice bath be?
• AS ColdPlunge ice bath chiller review
• Lay-Z-Spa Glacial Dip review: a budget tub with a filter pump
• Recovery hub