How to keep cold plunge water clean

A tub with no filter needs fresh water every few days. A chiller with a filter and a lid can go weeks between changes. Follow the maker's manual: the figures below are what to look for, not a set schedule.

What makes the difference

Feature	What it does
Cartridge filter	Catches hair, leaves and grit. Rinse it weekly and replace it as the maker says.
Ozone or UV	Built into some chillers. Ozone gas or ultraviolet light kills germs as water passes through, so you change it less often.
Lid or cover	Keeps out leaves, insects and rain, and keeps the cold in.
Sanitiser	A hot-tub style water cleaner. Some makers allow a small dose; others say water only. Check before adding anything.

Back to the list of sections ↑

Simple habits

1. Rinse off before you get in.
2. Keep the lid on between plunges.
3. Skim out leaves before they sink.
4. Drain and wipe the tub when the water looks cloudy or smells, whatever the calendar says.
5. In a hard frost, follow the maker's winter advice: some chillers must be drained or brought in.

Back to the list of sections ↑

Running cost

Refilling a 400-litre tub uses 0.4 cubic metres of water, a small amount on most water bills. The bigger cost is the chiller's electricity: chiller or ice has the sums. Every cold plunge page shows whether it has a filter and a lid, where the seller says.