How often to change hot tub water: a UK drain window

The cover comes off on a Friday, the water is still the fill from early summer, and the easy move is another jug from the hose to bring the line back up. That top-up hides the question in front of you, which is how often to change hot tub water. For a private garden spa, UK guides publish two rules of thumb: at least every one to three months, and every three to four months. The ranges differ, and neither figure is a statute for your patio. If the water is cloudy, foaming, or the test will not hold, you drain sooner. A holiday let runs on a much shorter clock.

The intervals come from Inflatable Hot Tub Guide's reading of BISHTA, from Best Pick UK, and from Total Chemical Solutions, plus HSE HSG282 for a business or a let, and Lay-Z-Spa's pack-away note on where treated water goes. We did not empty a tub, and there is no laboratory test. The shopping table is our inflatable hot tub comparison. A qualifying purchase through our links can earn a commission at no extra cost to you.

In short

For a private tub, treat one to three months and three to four months as two published rules of thumb, and drain sooner when the water looks or tests tired. Topping up replaces volume. A water change replaces the whole fill. A holiday let follows HSG282: after each rental or each week, whichever is shorter.

How often to change hot tub water at home

Start with how you use the tub, then put a date on the calendar. Inflatable Hot Tub Guide says change the water at least every one to three months, and it attributes that line to BISHTA, the British and Irish Spa and Hot Tub Association, sooner if the water is cloudy. Best Pick UK prints the same one-to-three-month span. Total Chemical Solutions prints a longer rule of thumb: every three to four months, sooner when use is heavy. A hot tub water change at three months sits inside both ranges. The months on either side do not.

Averaging them into "about ten weeks" would invent an interval none of the three pages states. If you only soak at weekends, and the water stays clear and the readings hold, the three-to-four-month line is the one that fits. If several people use the tub most evenings, heavy use pulls you toward the shorter span. A quiet fortnight does not restart a fill that has been sitting since spring.

BISHTA is a trade body, and the chemical page is a supplier's note. Your manual can ask for a shorter gap. On a small inflatable the water is a shared-bath volume. The Lay-Z-Spa Aruba AirJet, our top pick, claims up to three adults, prints 170 × 66 × 170 cm, and is about £394.74 on amazon.co.uk with 4.4 from 30 ratings. Three adults every night load that bowl faster than two people on a Sunday.

Signs the spa water is tired

The calendar is the backstop. Tired spa water tells you when that backstop is already late. Best Pick UK lists cloudiness, foam, a chloramine smell, and test readings that will not hold. Chloramines are what you smell when sanitiser has combined with sweat and other waste. A sharp indoor-pool smell under a cover that has been on all week is a reason to empty, even six weeks after the last drain.

Cloud needs one check before the hose comes out. A milky afternoon can be chlorine too low, or pH sitting where chlorine cannot work. The test order is in our hot tub chlorine and pH article. Correct the dose the label allows, run the filter, and look again the same day. If the cloud, the foam, or the smell returns once the reading was briefly inside the band, the fill is finished. Our cloudy hot tub water piece splits a chemistry miss from water that is simply old.

A collar of bubbles while the pump runs is what an air-jet spa is built to make. The Aruba listing claims 110 AirJets. Foam that stays once the jets are off, or that smells of sun cream, is waste. A shower before you get in slows that film. It does not add a month to water that already holds a scum line. Cold water because the heater was off is a heating job. Water that fails the test is a drain, even with a fortnight left on your date.

Topping up leaves the old fill in place

Evaporation, and the water you carry out on your shoulders, drops the line. Fresh water back to that line is ordinary care between changes. A top-up keeps the old fill in service. What leaves is mostly water. What stays has dissolved: sanitiser by-products, tap minerals, lotion, and whatever bathers add.

Guides call that remainder total dissolved solids, or hot tub TDS. A cartridge catches hair and grit. TDS stays in the water. Each top-up adds a little tap mineral and leaves yesterday's load behind, so the tub grows more concentrated while it still looks full. That is how a summer of topping up ends with chlorine that will not hold, one of Best Pick UK's drain signs.

These sources do not print one TDS cut-off, so there is no parts-per-million figure here. If your strips show TDS climbing while chlorine will not settle, plan the drain. With no TDS test, use the signs you can see and the two calendars above. Write the date inside the cover so a September soak has to answer to a start date in May.

Drain an inflatable hot tub to a foul sewer

When you empty the tub, send the water to a foul drain. Best Pick UK says to keep treated spa water off the garden if a foul drain is available. Lay-Z-Spa's pack-away note says treated water can kill plants, so it goes to a suitable drain. A lawn or a neighbour's fence line is a poor end for those chemicals, including water that still looks clear. A hot tub drain to sewer is the route both of those UK sources describe.

Follow the drain point in the manual and run a hose to an outside gulley you know joins the foul sewer. Keep the flow modest so the gulley does not flood the patio. A soakaway under the lawn is a different pipe. If you cannot tell which drain is foul, check with your water company before you empty a treated tub.

Do the filter in the same hour. Hose the pleats clean, and replace a crushed or slimy cartridge. The Aruba listing includes a type VI filter cartridge. New water and a filthy cartridge put part of the old fill straight back. Refill as a first fill, using the order on the setup guide. Reheating that cold water is part of the running cost. Check the water with a pool thermometer before a long soak. The listing's stated maximum is 40°C. Packing the shell away dry is the winter path, in storing an inflatable hot tub for winter.

A holiday let follows a shorter interval

If the tub sits in a house you let, HSE guidance HSG282 treats that setup as a business system, including a domestic inflatable. The interval is a water change after each rental or each week, whichever is shorter. Guests on a Saturday, and again the following Friday, mean you change with the booking. A household that never lets the house does not pick up that weekly duty from this section.

Paying guests are the case HSG282 is written for. The host's side sits in our hot tub in a holiday let article. Read HSG282 on the HSE site before you write a house manual. A competent person at the property still owns the control scheme. A family tub that is never let stays on the private rules of thumb, with an earlier drain when the water is tired. Leave the date where the next person to lift the cover will see it.