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 crops up in brochures about EM. It is 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, head under the surface, must 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.

Swimming water must be disinfected

Every swimmer brings microorganisms into the water: from the skin, mouth and nose, and sometimes traces of faecal 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 upsets. That is why pool water must not only be filtered but also remain disinfecting: it must be able to continuously neutralise 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 checked regularly. A pool used only by a family generally falls outside these rules, but not outside the risks: it is up to you to manage them, especially if children swim in it. Check the regulations that apply in your country.

Key points

Effective microorganisms are not disinfectants. They do not replace chlorine, bromine, salt electrolysis or any other disinfecting treatment for swimming 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 1 L per 10,000 L of water, from three times a season to once a week depending on how much the pool is used;
• EM ceramics placed in the sand filter, 500 g per 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 in circulation, but we do not endorse them.

What studies say

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

In fact, the reasoning points rather the other way:

• Chlorine kills microorganisms, including those in EM. EM manufacturers themselves advise against mixing them with chlorinated water. In a properly chlorinated pool, added EM do not survive for long.
• An EM product adds organic matter (fermented molasses, plant extracts). 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, and likewise in the United Kingdom, 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 authorised. No EM product has this status. To find out more, read our guide EM and regulations.

Did you know?

The stinging "chlorine" smell does not 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 renewing 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 bubbles throw up fine droplets that people breathe in. A spa must always be disinfected according to its manufacturer's instructions, with frequent checks. EM and ceramics replace nothing there.

If you still want to use EM

You can use EM around the pool, provided you keep your usual treatment and never reduce it on the strength of a promise.

• Around the pool: EM Clean multi-purpose cleaner, diluted as directed, is suitable for cleaning the pool surround, coping stones, plant room or the cover once removed. Our usage tips are in the guide Natural cleaning with EM Clean.
• In the water: if you are determined to try EM Clean in the pool, never do so during a shock treatment, and then 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 offered 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, with test strips or a testing kit. Note the pH and disinfectant level: it is 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 genuine 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 present microorganisms consume the nutrients. There is no disinfecting treatment, and you accept living water, never sterile, with a little algae and small wildlife.

This type of pool has to be designed from the outset, with a large planted area and precise sizing. You cannot 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, call on a professional who specialises 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 swimming 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 replace nothing either. If you really want to do without disinfectant, turn to a natural swimming pool designed for the purpose.

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