How often should I change cold plunge water?

Follow your tub's maker. Renu Therapy advises water changes every 4 to 6 months or as necessary for its filtered, ozone-equipped tubs. A tub with no filtration needs changing far more often.

Do I need chemicals in a cold plunge?

It depends on the tub. Renu Therapy says its built-in ozone generator and filter remove the need for chemicals, and sells its treatment kit as an option.

How often should I change the filter?

Renu Therapy says its standard filters last 2 to 6 weeks in home use, and most customers change them every 2 to 3 weeks.

Cold Plunge Water Maintenance: A Simple Schedule

Water care is the least exciting part of owning a cold plunge. It’s also the part that decides whether you want to get in.

This article sets out a schedule. For the other accessories, start with the cold plunge accessories buying guide.

Short answer: change the filter on the maker’s schedule, test weekly if you use chemicals, and drain when the maker says or when the water looks or smells off.

Start with what your tub does for itself

Here’s what the spec sheet won’t tell you: there’s no single schedule, because tubs differ.

Renu Therapy says every one of its units has a built-in ozone generator and a 50-micron filter, and that this removes the need for chemicals. An inflatable ice bath has neither. Read your manual before you copy anyone’s routine.

A schedule for a filtered tub

These figures are Renu Therapy’s, for its own tubs.

Task	How often	Source
Change the filter	Every 2 to 6 weeks; most owners every 2 to 3	Renu FAQ
Replace the mineral stick	About every 3 months	Renu product page
Replace oil and dirt buoys	Every 1 to 3 months	Renu FAQ
Change the water	Every 4 to 6 months, or as necessary	Renu FAQ

Heavier use shortens every interval.

If you add a treatment kit

The Renu Pure Water Treatment Kit ($75) has a sanitizer, an oxidizer, and 25 test strips. Its published dosing is:

At each fill: 2 teaspoons of sanitizer and 2 teaspoons of oxidizer.
Each week: 1 teaspoon of oxidizer.
As needed: more sanitizer, based on the test strip.

Follow the label on the product you own. Doses differ between brands and tub sizes.

What to test for

CDC recommends a pH of 7.0 to 7.8 for pools and hot tubs. It explains that as pH rises, chlorine gets worse at killing germs, especially above 8.0.

That guidance is written for pools and hot tubs, not cold plunges. It’s still the best public reference for pH. Renu’s strips print a target of 7.2 to 7.8.

Signs to act early

Cloudy water, a film on the surface, or a smell are reasons to test and treat now. My rule of thumb: if you’d hesitate to put your face in it, don’t wait for the schedule.

Cold isn’t clean

You get slower upkeep with cold, filtered water than with a hot tub. You don’t get to skip it. Renu still lists filter changes every few weeks on tubs it says need no chemicals.

For tubs with no chiller or filter, see the ice bath buying guide.

Bottom line: the filter does most of the work. Change it on time, and the rest of the schedule is light.

Sources

Renu Therapy FAQ (filter interval, ozone system, water changes, buoys and sticks), accessed October 8, 2026: renutherapy.com
Renu Therapy, Pure Water Treatment Kit and Sanitizing Spa Stick listings (contents, dosing, lifespan, price), checked September 2026
CDC, “Home Pool and Hot Tub Water Treatment and Testing,” May 10, 2024: cdc.gov

Not medical advice.This page is general product information. Heat and cold exposure aren't safe for everyone. Talk to a physician before starting a sauna or cold plunge routine, particularly if you are pregnant or have a heart, blood pressure, or circulation condition. See our Editorial Policy.