EM and swimming pools: what we really know about effective microorganisms in pool water

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"A chlorine-free pool thanks to microorganisms": this promise often shows up in brochures about EM. It's appealing, because nobody likes the smell of chlorine or stinging eyes. But a swimming pool is not a garden pond, and water you swim in, with your head under the surface, has to stay safe.

We sell EM products and ceramics that some people use around their pool. So we owe you a clear answer: what manufacturers suggest, what studies say, what the law says, and what you can reasonably do.

Pool water must be disinfected

Every swimmer brings microorganisms into the water: from the skin, mouth, and nose, and sometimes traces of fecal matter. Warm, well-lit water rich in organic matter suits them very well. Some germs commonly found in poorly maintained pools cause ear infections, skin infections, or digestive problems. That's why pool water must not only be filtered but also remain disinfecting: it has to be able to continuously neutralize whatever swimmers bring in.

Pools open to the public are subject to health and safety rules in most countries: their water must be filtered and disinfected, and it is inspected regularly. A pool used only by one household generally falls outside these rules, but not outside the risks: it's up to you to manage them, especially if children swim in it. Check the regulations that apply where you live.

Key takeaways

Effective microorganisms are not disinfectants. They do not replace chlorine, bromine, saltwater chlorination, or any other disinfecting treatment for pool water.

What manufacturers suggest

In its literature, the EM manufacturer describes a pool treatment combining two elements:

• a liquid EM such as EM Clean, at about 1 quart (1 L) per 2,640 gallons (10,000 L) of water, anywhere from three times a season to once a week depending on how much the pool is used;
• EM ceramics placed in the sand filter, 1.1 lb (500 g) per 2,640 gallons (10,000 L), claimed to remain active for at least ten years.

According to the manufacturer, this treatment would reduce organic matter, algae, and germs, and allow chlorine use to be cut sharply. We report these claims because they are circulating, but we do not endorse them.

What studies say

We looked for independent trials measuring the sanitary quality of pool water treated with EM: we found none. No published data shows that an EM product keeps pool water free of dangerous germs.

In fact, the reasoning points the other way:

• Chlorine kills microorganisms, including those in EM. EM manufacturers themselves advise against mixing their products with chlorinated water. In a properly chlorinated pool, added EM don't survive for long.
• An EM product adds organic matter (fermented molasses, plant extracts). And chlorine reacts with organic matter: it gets used up instead of remaining available to disinfect.
• Trials carried out in natural water with EM balls show that a fermented organic input can also add bacteria and nutrients. We go into detail in our guide on pond balls.

Finally, the law settles part of the question. In the European Union, a product presented as able to destroy or control germs or algae in pool water is a biocidal product. It must contain approved active substances and be authorized. No EM product has this status. To learn more, read our guide EM and regulations.

Did you know?

That stinging "chlorine" smell doesn't come from too much chlorine, but from chloramines, which form when chlorine reacts with sweat, urine, and other matter brought in by swimmers. Showering before swimming and regularly replacing some of the water help limit their formation.

Take extra care with spas and hot tubs

What applies to pools applies even more to a spa or hot tub. The water is warm, small in volume, and shared by several people. Some bacteria multiply quickly there, and the jets spray fine droplets that people breathe in. A spa must always be disinfected according to its manufacturer's instructions, with frequent testing. EM and ceramics don't replace any of that.

If you still want to use EM

You can use EM around the pool, as long as you keep your usual treatment and never cut back on it based on a promise.

• Around the pool: EM Clean multi-purpose cleaner, diluted as directed, works well for cleaning the pool deck, coping, equipment room, or the cover once it's removed. Our usage tips are in the guide Natural cleaning with EM Clean.
• In the water: if you're set on trying EM Clean in the pool, never do it during a shock treatment, and afterward check that your disinfectant level stays within the range recommended by the manufacturer of your treatment.
• Ceramics: beads such as our pink EM ceramic beads are marketed for natural ponds and swimming pools. They are fired ceramic objects with no living microorganisms. They do not disinfect water: see our guide on EM ceramics for what to make of them.

Emy's tip

Test your pool water at least once a week during the season, and after every period of heavy use or every storm, using test strips or a testing kit. Write down the pH and disinfectant level: it's the only way to know whether your water is really safe.

Natural swimming pools: a different model

If you dream of water free of disinfectant, there is a real solution: the natural swimming pool, also called a swimming pond or biological pool. It works on a different principle. The water circulates through a planted regeneration zone and biological filters, where plants and naturally occurring microorganisms consume the nutrients. There is no disinfecting treatment, and you accept living water, never sterile, with a little algae and some small wildlife.

This type of pool has to be designed that way from the start, with a large planted area and precise sizing. You can't turn a conventional pool into a natural swimming pool by pouring EM into it. When open to the public, these pools are also subject to specific health rules. For a private natural pool, hire a professional who specializes in this type of installation.

In summary

Pool water must remain disinfecting, because swimmers constantly bring germs into it. EM are not disinfectants, no independent study shows that they make pool water safe, and chlorine destroys them. Use them instead to clean around the pool, keep your usual treatment, and test the water every week. Ceramics don't replace anything either. If you really want to do without disinfectant, look into a natural swimming pool designed for that purpose.

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