When should I change my spa water?

Do you know when to change your spa water? In this article, you'll learn the signs when to change your spa water and keep your spa fresh and clean for a safe, relaxing soak.

heated spa pool

Wondering when it's time to change your spa water? In this aticle, we'll guide you through the process of knowing when to change your spa water and what signs to look out for.

This article covers:

How often should I change the water in my spa?

As a rule, you should change the water in spas containing 700L to 4000L on average every 3-6 months for an average user and sooner for heavy users.

An average user would use their spa 2-3 times a week. A heavy user would use their spa 4-5 days per week.

How often should I change the water in my swim spa?

Swim spas containing 5000L to 7000L will need to have the water changed on average every 12-18 months for an average user and every 8-10 months for heavy users.

Watch: How to drain your Vortex™, Arcadia™ or Fisher™ Spa

How long can you leave spa pool water in?

When determining your spa pool refill schedule there are several factors to consider including the bather load of your spa pool, how frequently it is used and how well your bathers take care not to introduce contaminants into the water. The size of your spa pool is also an important factor

Although the general rule for changing spa pool water, for a spa size of between 700 - 4000 liters of water, is every 3-4 months, you may need to change your water more regularly if your spa pool is in heavy use. For perspective, average use is 2-3 days per week and heavy use is 4-5 days per week.

To keep your water fresh for longer, try to avoid introducing contaminants into the water as much as possible. Some contaminants, also known as dissolvable solids, aren’t possible to avoid, such as sweat and dead skin cells, while others, such as beauty products and detergents, can easily be limited.

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Things that can build up in your spa or hot tub water

Girl in spa

Body oils

Body oils are oils secreted by skin cells that wash off into the spa water upon bathing. These naturally occurring oils build up over time and can form an oily film on the water surface, causing foam, and can line the inside of the spa plumbing, restricting water flow.

Suntan lotions & Beauty products

If bathers climb into your spa pool without showering first, you run the risk of introducing chemicals and contaminants to your spa water including beauty products, such as make-up and hair spray, and lotions, such as suntan lotion. These products build up and contribute to cloudy water and foam.

Household cleaning products

When bathers use the spa pool wearing freshly washed bathing suits, the material may still have some laundry detergent in the fabric, contributing to chemically saturated water.


When spa pools are used for a while and left to stand unused with contaminated water, algae can grow in the water and inside the spa pool plumbing. Keeping the cover on too long can also contribute to algae. Algae contribute to smelly and cloudy water as particles float around the system or coat the inside of the spa.


The main cause for concern in old or dirty spa pool water is the build-up of bacteria in the water. When left untreated, bacteria growth can pose a significant health risk including skin rashes and bacterial infections.

Organic matter

Naturally, bathers will introduce organic matter into the spa pool such as dead skin cells, hair, and other organic particles. Due to the chemicals in spa pools, this matter breaks down in the water. However, over time, these particles contribute to the TDS (total dissolvable solids) in the water and cause cloudiness, foam, and odor.

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How do you know when to change your spa pool water?

There are many telling signs that let you know your water is old or oversaturated with TDS and in need of changing. Some signs that its time to change out that water include:

  • Foamy water: Often the first sign of water in need of changing is foam when running the jets of your spa pool. Foam is caused by a build-up of surfactants such as detergents, oils, beauty products, and even spilled drinks. Foam can also be caused by low calcium levels in water and unbalanced pH or alkalinity, rule these out with test strips before changing the water.
  • Smelly water: A key warning sign of water that needs to be changed is a foul smell. When your spa pool water smells off, it is likely due to a build-up of bacteria, algae, and other contaminants that could potentially cause you harm.
  • Cloudy water: A build-up of contaminants or TDS can cause water to appear cloudy or murky. If your spa water does not clear up completely after shock treatment, the water is too far gone and needs changing.
  • Discolored water: When your crystal blue water changes to a darker hue there may be an accumulation of algae or bacteria in the water. This may not seem like a big problem but left untreated, the water could potentially cause skin irritation or bacterial infections.
  • Old water: If you check your calendar and it’s been over 4 months since you last renewed your spa pool water, it might be time. Old water can become over-saturated with chemicals and dissolved solids, leaving water feeling less fresh than it should.

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My water looks clear so what is the problem?

If your spa pool is long overdue for a water change but the water still looks fresh, it is always better to be safe and change the water. Chances are there is a hidden build-up of contaminants, or an unbalanced pH waiting to irritate your skin. It’s what you don’t see that can be dangerous!

Even if your spa water is clear, bacteria are microscopic and may still be abundant in the water. The old spa water may even house parasitic illnesses, E. coli, and cause folliculitis.

Your spa pool may also not show when the pH and alkalinity are out of balance, or when the water is too soft to safely bathe in and enjoy, with low calcium and surface tension causing damage to your spa system and provoking skin rashes. After all, if the water is older than 4 months with frequent use, refreshing the water will take your spa experience to the next level.

Key tips for making your spa water last longer:

  1. Always shower before entering your spa or swim spa.
  2. Keep your spa filters clean.
  3. Keep your water balanced.
  4. Use a good quality spa sanitiser and shock.

Frequently Asked Questions

Can I empty half of my spa water and refill it to keep the water longer?

No. It is better to use a spa pipe degreaser and then empty the spa and refill it with fresh water.

What happens if I don’t change my spa water?

Leaving your spa water unchanged when it is showing signs of over-saturation and bacteria growth can leave your spa water susceptible to worsening conditions, such as excessive foam and foul-smelling water, as well as potentially posing serious health risks such as folliculitis, E.coli infection, and parasitic illnesses.

Why do I need to empty my spa water?

You need to empty your spa water from time to time to clean the shell of your spa pool and the filters, before refilling the spa with fresh water to ensure a safe, and healthy spa soaking experience.

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Got more questions?

Talk to us or email us your spa questions and we'll be happy to help!

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