Is your spa pool water clean?

We shopped in-store and online for spa water treatment products to keep bacteria out of the hot tub.

Nasties like legionnaires, a bacteria which can lead to a lung infection similar to pneumonia, can develop if the water isn’t kept clean, along with other germs which can make you sick.

We assessed 13 products on whether spa pool owners would be able to meet the New Zealand Standard for pool water quality using the products. While the standard is compulsory for public pools, it’s a voluntary standard for private ones. However, we would expect manufacturers to sell products that meet the standard for all spas.

While four products would be able to meet standard, for the rest, you’d need to add another cleaner to make the water safe.

So, how do you know what disinfectant to use so you can soak in clean water?

We take you through the range of disinfectants available and how to keep nasties out of your hot tub.

Legionnaires traced to spa pools

In the past five years, there have been 39 cases of legionellosis from people who have reported using or cleaning a spa pool, a spokesperson from the Institute of Environmental Science and Research (ESR) said.

Since 2020, there have been two outbreaks of the disease where a spa pool was the source.

Legionnaires’ disease is caused by breathing in airborne particles carrying legionella bacteria from soil or contaminated water. 

Water also gets dirty from bathers bodily fluids, which can lead to gut, ear and skin infections, even E.coli and urinary tract infections.

Dirt can also get blown into the spa which could lead to algal blooms.

An effective water treatment should keep these nasties out of the water.

Spa pool water treatment results

Traditional water treatment: chlorine, bromine and hydrogen peroxide

The traditional water treatment products for spas are chlorine or bromine.

Three products we shopped for contained either (or both) of these chemicals and were suitable to keep water clean, according to the NZ Pool Water Quality standard (see Table).

The fourth product, Clarity Spa Radiance, contains a source of chlorine (sodium dichloroisocyanurate dihydrate) which also met the standard.

Hydrogen peroxide sanitisers can also be used for those who want a chlorine alternative.

Yet, the three hydrogen peroxide cleaners we checked didn’t have the required dosage to meet the standard (see Table).

The spokesperson for the two Poppits products we surveyed provided evidence that its products meet the Australian pool safety standards and are registered as sanitisers.

However, the water engineer we consulted with for this story recommended the products should be used with a sanitiser and algicide to make the water safe.

Alternative water treatments: silver

The other products we shopped for touted claims of being “environmentally safe” or that they could replace “harsh toxic chemicals”.

Two of these products contained colloidal silver or silver oxide. None of them would be appropriate to clean the water on its own.

There is no recommended concentration for products containing silver in the NZ pool water quality standard. If it is used, the pool owner would need to do regular microbiological testing to show it is keeping the water clean.

Yet one of the products – SimpleSilver – says it meets the NZ pool water quality standard and that no other products are required. We don’t believe this to be the case.

In 2021, SimpleSilver was linked to a case of legionnaires. At the time, the company said the spa pool’s filter must be kept running and cleaned with an approved filter sanitiser.

Yet, claims like “one step – once a year” and “no other products required” create a different impression.

The Salud Silver Cove Spa Pool Sanitiser also gives the impression that it’s a low-maintenance product with no need to test water or balance pH.

Yet, if the spa pool is being used often, you may also need to use an oxygen-based shock product, a Salud spokesperson said.

The Zodiac Nature2 Spa Stick is a bit more upfront. It states that using its system of “silver, zinc and copper to kill bacteria and algae” will reduce chlorine requirements, rather than replace them completely.

‘Natural’ treatments

The “natural” or “eco-friendly” treatments we looked at would not be suitable for keeping your spa pool water clean.

Biologica Spa Alchemy Natural Water Treatment says it “Keeps your spa water clean and clear, and help keeps it in balance.”

Yet, the product is not a sanitiser, a Biologica spokesperson said. It’s “an additive treatment that radically reduces spa water maintenance.”

The product also recommends that the water is dosed with chlorine or bromine at least once a week, depending on how often you use the pool.

Biologica didn’t provide any independent evidence to back up its natural, biodegradable and sustainable credentials.

Spa Magic markets itself as a chlorine-free alternative. “No more dangerous chemicals” and “non-toxic” as well as “eco-friendly”.

It’s also labelled as “Doctor’s Choice” and a “Single Dose Spa Treatment that lasts for up to 3 months” that can be used as a substitute for chlorine.

Yet, our expert said it shouldn’t be used as a standalone product to keep your spa pool water clean, and it doesn’t meet the NZ standard.

In the fine print, Spa Magic does say the product can be used with chlorine and bromine.

Water’s Choice Pure Enzymes for Spas reckons its product is the “minimalist approach to treating your pool or spa water”.

Yet, you still need to add sanitizer to the pool water to keep it clean rather than use it as a standalone product.

What different spa products do

There are a lot of products for spa pool water, but it can be confusing to know what each of them do and whether you need them all.

Here’s a quick guide to spa pool water treatment:

Sanitizer: to disinfect your spa water, you need a sanitizer like chlorine or bromine. There are other options like hydrogen peroxide, however, before you buy, check what’s in them, and ask for evidence the product is effective at killing bugs in your spa pool.

Shock: if your spa has had more bathers than usual, a shock treatment (a dose of chlorine) can help clear the water and kick-start the sanitizer.

Alkalinity: measures the level of carbonates and bicarbonates in the pool, which helps to stabilise the pH.

pH level: if the pH level in your spa is too high the chlorine won’t work as well as it should. It’s also important that the pH of a bather’s body is in the same range as the pool water to avoid irritation to the skin and eyes from the sanitizer. The NZ Safety Standard recommends a pH between 7.2 – 8.

You can buy test strips to check the pH level is correct.

Water hardness: refers to the level of calcium in your spa pool. If you have too much, the water will be hard, and if you don’t have enough, it’ll be soft.

Too much calcium can lead to a build-up of calcium in the workings of the spa. While if it’s too soft, the water will feel a bit slimy and create a foam, and could lead to corrosion of the pool.

You can buy test strips or a test kit to measure water hardness. If the level is too high, you’ll need to empty the spa and give it a good clean.

Enzymes: can help to keep spa pool water clean, but they should be used in conjunction with a sanitizer. Enzymes work by helping to break down organic matter in the water, like lotions, sweat and body oils.

Keeping your spa pool filters clean

Along with chemical treatment, spas also need filtration to keep the water clean.

Filters act like sieves to remove particles from the water. The efficiency of the filter can also depend on the pump. If your spa has a low-flow pump, the water isn’t going through the filter as often, and so isn’t cleaning the water as often.

How often should you change spa pool water?

How often you need to change the water in your spa depends on:

• how often you use it
• whether users have a shower before jumping in
• how well you keep the water chemically balanced and clean.

New Zealand Standard for pool water quality recommends changing the water every month. Once empty, the spa will need a good scrub before being refilled.

Because chemical treatments are used to keep spa pool water clean, it needs to go through the sewer system (not a storm drain).

It’s recommended that you check the level of chemicals in the water at least once a week. If your spa has lots of bathers, you may need to increase the frequency of testing. You should also clean the filters at the same time.