How Often to Change Hot Tub Water – A Comprehensive Guide

Michael Keenan


Hot Tub Maintenance

Hot tub owners sometimes think that adding chlorine to the water is enough to keep it safe and healthy. Good chemical management is important, but with a hot tub you do need to change the water periodically.

It’s important to change the hot tub water regularly for both health and hygiene reasons, as well as to prevent corrosion of the tub itself. In this article, we’ll discuss why it’s important to change hot tub water and how often it should be done.

We’ll also take a look at other signs that might indicate when your hot tub needs its water changed. Further information about TDS levels and supersaturation are also included. Don’t worry, it’s all very straighforward.

Keep reading to find out more!

how often to change hot tub water

Quick Answer:

You should change your hot tub water every 3-4 months, depending on the size of the hot tub and how much it’s used. This helps keep the water clean, balanced and safe for use. Signs that your hot tub water needs changing include foam or bad smells, or if it has been a few months since the last drainage/refill.

Regular changes also help prevent scaling and increase sanitizer efficiency. Make sure to track your last water change date so you know when it’s time!

How Often Should You Change Hot Tub Water?

This is a common question we are asked and the answer to this is that typically, the hot tub water must be drained and refilled every 3 to 4 months.

However, the frequency will depend entirely on your hot tub usage (or load), how many people are using the tub and how often the hot tub is used. You can estimate how often to change the water in your hot tub by doing a bit of math.


You need to first know how much water your hot tub holds or its volume. We do some of that math for you below.

  • A hot tub for 2 people holds around 170 gallons or 650 liters of water.
  • A hot tub for 4 people holds around 330 gallons or 1,250 liters of water.
  • A hot tub for 7-8 people holds around 475 to 610 gallons or 1,800 to 2,300 liters of water.

You can check the exact capacity of your particular hot tub by referring to the manufacturer’s manual or website. Smaller hot tubs holding less water need to be changed more frequently compared to larger hot tubs.

Number of People

The number of people using the hot tub, or the bather load, is another parameter required to calculate the frequency of water change. Just having an estimate of the bather load is sufficient.

Formula for Water Change

Finally, divide the volume of the hot tub by 3 and then divide this by the bather load. For example:
Volume of hot tub / 3 / average bather load = Frequency of water change

  • 170 gallons / 3 / 2 = 28 days
  • 475 gallons / 3/ 2 = 79 days

However, you must remember that this is just a guideline of how often to change the water in your hot tub. Remember, the greater the volume of water in your hot tub, the less often you’ll need to change the water. Think of this as a diluting effect!

The timing of water change may vary depending on other factors such as the location of your tub (outdoors or indoors), the quality of water in your area, how you maintain your tub between the water changes. Is your spa or tub exposed to the weather or is it covered when not in use?

For areas that have cold winters many chose to winterize their hot tubs and close them down for the coldest months.

When you are changing the water it’s a good time to give the hot tub cover a quick clean!

change cycle for healthy spa water

Other Signs Indicating Water Change

Some other signs indicating that it may be time to change the water in your hot tub include:

Foamy Water

Bubbles in the hot tub are normal; however, if you see that the water in the hot tub is looking foamy, this is not a good sign. You can remove the foam by using an anti-foam solution or foam remover.

If the foam does not clear out, then you may need to change the water. Also, if the water in the hot tub is cloudy, discolored or funky, then you can try using a hot tub shock to clear the water. If the water doesn’t clear, then you must change the water immediately.

Smells Bad

Typically, the hot tub should not have any smell, except for the smell of chlorine if you have added some to the water.

However, if you find that the hot tub water is starting to smell bad, then something is definitely not right and could be because of a problem in the plumbing, bacteria, algae, or mildew and the only way to get rid of the smell is to change the water.

Green, smelly water in your hut tub? – find out how to fix that problem now.

Check the Date

Make a note of when you last drained your hot tub and refilled it. This will help you keep track of your hot tub’s maintenance. And, if the last water change was done a few months ago, then it may be time to change the water.

Why You Should Change the Hot Tub Water

If you keep using your hot tub for several months without changing the water, there could be problems such as:


The hot tub water can only hold a certain number of dissolved substances, beyond which it will become supersaturated. Typically, the water contains dissolved calcium that is present in the form of calcium chloride, also known as calcium hardness or water hardness.

If you don’t change the hot tub water for a long time, then the water will become supersaturated and will not be able to dissolve any more calcium chloride. This will then start forming scales in the filter, fixtures of the hot tub and also in the pump.

Signs that this is happening can include seeing white flakes in your hot tub water. And, too much scaling can cause damage to the equipment and surfaces, resulting in costly repairs.

Total Dissolved Solids (TDS)

Each time that you use your hot tub, you leave behind TDS (total dissolved solids) such as sweat, body oils, makeup, body lotion, perfume, shampoo and other bodily matter, which contaminate the water.

The sanitizer you add to the water can only work to a certain extent and a high TDS level and supersaturation can prevent the sanitizer from mixing with the water and disinfecting it effectively.

The water will become gritty, murky and even develop a bad smell. Then, even if you add a sanitizer, it will not help to clean the water and you’ll be just soaking in unclean water, which can be extremely unhealthy.

So, it is very important to change the water in your hot tub regularly. It’s also a good idea to keep track of the TDS accumulating in the water by using a TDS meter between the water changes.

relaxing in clean hot tub water

Common Questions

What is supersaturation and why is it important to avoid in a hot tub?

Supersaturation occurs when the hot tub water exceeds its capacity to dissolve substances like calcium chloride and starts forming scales in equipment and surfaces, leading to costly repairs.

What are Total Dissolved Solids (TDS) and how can they affect the cleanliness of my hot tub?

Total Dissolved Solids (TDS) are contaminants such as sweat, body oils, makeup, etc., that build up over time in the water and can lead to murky waters with a bad smell even with sanitizer added.

Parting Thoughts

It is essential to change the used, old, dirty water in your hot tub and replace it with fresh water on a regular basis. This will ensure that you’re able to soak and relax in a clean hot tub that is safe and healthy to use.

Regularly changing hot tub water helps keep you healthy, prevents corrosion of the tub, and ensures that your sanitizer is working properly so you can soak in clean and safe water!

michael keenan author

Author - Michael Keenan

I'm Michael Keenan the owner and creator of the Outdoor Care Guide. I'm a trained horticulturist with over 30 years of experience in pool care, plant care, and landscape care! Seemed like a good idea to share - I think I can make your life easier and save you some time and money!