How Often Should You Drain Hot Tub Water? (5 Signs)

You’ll find a lot of conflicting information online about how often to change hot tub water. I’m a little fanatical about keeping my water clean, which is why I’ve never had any problems. I want to share with you my tried and tested guide so your water is as fresh as mine.

A general rule of thumb is that hot tub water needs to be emptied and changed every 3 to 4 months. The exact frequency depends on the number of bathers and the amount of usage the hot tub gets on a weekly basis. Signs that it’s time to drain the water include high TDS and cloudy, foamy, or smelly water.

This detailed guide will show you:

  • Telltale signs it’s time to drain your water
  • How partial refills can keep your water fresher
  • How to calculate your exact water drain frequency

How do I know when to drain my hot tub water?

While hot tub water must be drained every 4 months as a minimum, heavy usage may mean a more frequent change. Here are the signs that indicate it’s time to drain and refill with fresh water.

High TDS

Performing a total dissolved solids (TDS) test is one of the most accurate ways of assessing whether it’s necessary to drain the water.

A TDS reading above 1500 parts per million (ppm) is an indicator that it’s time to drain your hot tub water.

All you need for carrying out a TDS test is these test stripsOpens in a new tab. from Amazon. The test will provide you with a reading of how saturated your water is.

While it’s possible to get away with readings up to 2000 ppm, it’s best to avoid letting it get above 1500 ppm.

When your TDS becomes too high, the chemicals become less effective, which leads to other signs such as cloudy and foamy water.

Cloudy water

Cloudy water is one of the most common signs that the water needs to be drained. The reasons why hot tub water becomes cloudy are a high pH, high alkalinity, low sanitizer, or dirty filters.

If your filters are dirty or haven’t been replaced in a long time, they are no longer able to filter the particles of dirt and grime in the water, which leads to cloudy water.

If you think the cause has been the dirty filters, you might be able to get away with a partial water change, which is something I’ll discuss later on.

Use this special filter cleanerOpens in a new tab. every month to clean and keep things working properly. As filters age, the filter cleaning product becomes less and less effective.

Once you get to the stage that it’s no longer possible to keep them clean, you must replace the filters with new onesOpens in a new tab..

Before emptying the hot tub, shock the water with this chlorine shockOpens in a new tab. or oxidizer. If that doesn’t work, then it’s definitely time to refill with fresh water.

Foamy water

Hot tub foam is caused by debris, body care products, low calcium hardness, and a high or low pH. The older your hot tub water, the harder it is to sanitize.

Turning on the jets when there is a build-up of dissolved solids in the water causes foam to appear on the surface. The dissolved solids in the water “attach” themselves to the air bubbles blown by the jets. Given enough time, the bubbles start to group together, which results in a layer of foam.

The first thing to do when the water is foamy is to use this de-foamerOpens in a new tab. from Amazon. It should clear up the problem so that you can carry on enjoying your hot tub.

But if the foam returns soon after adding the de-foamer, it means it’s time to drain the water, clean, and refill.

Smelly water

If you notice a foul smell coming from the hot tub as soon as you remove the cover, then you must drain the water immediately.

Healthy spa water shouldn’t have any smell whatsoever, not even a “chlorine” smell. Smelly water is caused by a build-up of bacteria, mildew, and biofilm in the plumbing.

Do not attempt to remedy the problem by adding more chemicals or partially replenishing the water. No amount of shock will get rid of the smell. The only option is to drain fully and fill with fresh, clean water.


Make sure to drain the water in your hot tub at least every 4 months. If your hot tub gets used a lot by several different users, it’ll need changing more frequently.

I’m going to show you how to calculate the exact frequency for your hot tub at the end of this guide.

Make a note somewhere each time you empty the hot tub so you know exactly when it’s due again. In the meantime, you can perform partial water changes to keep things as fresh as possible.

Partial water changes

You can avoid full changes by partially draining the water and replenishing it on a frequent basis.

Partial water changes are handy for those that use their hot tub a lot. They’re also a good idea if you live in a cold climate. Partial changes prevent the risk of freezing that may occur happen during a full water drain.

Remove a portion of your water (around half) and check the TDS level using strips or a handheld meter. Using the reading, adjust the TDS until the water is balanced and below 1500 ppm.

Why perform partial water changes?

Low TDS levels make it easier to balance the water chemistry and increase the efficiency of your sanitizers. Here is an illustration of why high TDS levels reduce the efficiency of sanitizers:

Imagine adding a teaspoon of salt to a glass of water and giving it a stir. What happens? The salt dissolves.

But what happens if you keep adding salt? Eventually, the salt isn’t able to dissolve because the water is too “full.” The water has lost its dissolving “power.”

When the TDS is high, your hot tub water no longer has the power to absorb any of the chemicals that you add, rendering them useless.

This is why it’s such a good idea to perform partial water changes. It’s easier to balance the water chemistry, ensuring that the water remains cleaner and fresher.

How to calculate water drainage frequency

Using a simple bit of math, you can calculate the exact amount of days until your next water change. Great, right?

The first piece of information you need is your hot tub’s water capacity in gallons. Check with the manufacturer or owner’s manual to find out exactly how many gallons your spa holds.

Next, estimate how often you use your hot tub: twice or less per week or 3 or more times per week.

Now, add up the number of people that use the hot tub on a regular basis. Try to come up with an average over a typical 4-month period.

Now we have the figures for the water volume and bather load, we can get down to the math. For my example, I’m going to use an average-sized 300-gallon hot tub used 3 or more times per week by 2 people on average.

First, divide the hot tub capacity by:

  • 2 if the hot tub is used twice or less per week.
  • 3 if the hot tub is used 3 or more times a week.

Secondly, divide that figure by the number of users.

The resulting figure is the frequency (in days) with which you need to fully empty and change the water. Here is the calculation:

Hot tub volume of 300 gallons divided by 3 = 100.

100 divided by 2 users = 50.

The calculation shows that the water needs to be drained every 50 days.

Remember that this is to be used as a guide only. Depending on the size of your hot tub and the number of users, the resulting figure might be more than 120 days.

However, never go more than 120 days (4 months) between refills. Even if you don’t use the hot tub frequently, or you carry out partial water changes, 120 days is the maximum.

Joshua Milton

Joshua Milton is a seasoned hot tub enthusiast. With many years of experience in the industry, he offers valuable insights on hot tub maintenance, health benefits, and relaxation techniques.

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