By The Zagosa Team. Published .
Reviewed or updated .
Yes, nearly every UK hot tub is filled and topped up straight from a mains-fed garden hose. Just keep two things in mind: how hard your local water is, and what state the hose is in. A 20-pound hose-end pre-filter deals with most of what can go wrong.
What the hose can introduce
An old rubber hose that has baked in the sun for a season can leach plasticisers and grow biofilm inside the bore. The first water out of it should never reach your tub. Run it onto the lawn for 30 seconds first.
A new food-grade hose (often sold as a caravan hose) is worth keeping purely for tub top-ups. Twenty pounds, lasts years, never touches the lawn. The water smells and tastes noticeably cleaner.
What the mains can introduce
The south-east has very hard water. A refill there can push calcium hardness above 400 ppm before you have added a single chemical. Parts of Scotland and the North West have very soft water, which brings its own trouble, as it strips calcium off the heater element.
A hose-end pre-filter (a small carbon and resin canister that screws onto the hose) removes chlorine, metals and a slice of the hardness. They last about three refills and cost roughly 15 to 20 pounds, paying for themselves in chemicals saved on the first fill.
Topping up without throwing the chemistry off
Top up through the filter housing rather than the open shell. That way the mains water is dispersed and filtered as it comes in, instead of landing as a cold puddle on the floor of the tub.
Dose for the volume you added, not the whole tub. A 50-litre top-up does not need a full sanitiser dose, just a quick check and a small adjustment.
Retest an hour later with the jets running. The fresh water needs to mix before any reading means much.
Common questions
Can I use rainwater from a water butt?
No. Rainwater carries leaves, insects and atmospheric pollution, and it is not chlorinated. The saving is not worth the chemistry chaos.
Should I run hot water in?
Mixing in hot from the kitchen tap can shave hours off a winter refill, but never run a domestic hot supply through a garden hose. The plasticisers leach faster at temperature. Use a clean bucket instead.