When the dragonflies emerge and the water turns the color of strong tea in the early evening, a certain kind of silence descends upon a natural pool. It’s lovely. Additionally, it’s either completely safe or a slightly risky experiment in relying on nature to do a chemist’s job, depending on who you ask. Even after years of demonstrations, garden designer Tom Hoblyn, who constructed one in his own backyard nine years ago, has yet to convince a single customer of the concept. When the marketing brochure ends and the questions begin, that fact alone reveals something about people’s true attitudes toward safety.
The pitch is sufficiently alluring. No chemical runoff into the soil, no stinging eyes, and no chlorine. Microorganisms maintain some sort of biological equilibrium in the water, plants and gravel beds filter the water, and the system as a whole is meant to function similarly to a healthy pond, albeit more neatly. It’s a beautiful concept. Nearly all of the information that most homeowners never consider asking about before signing a contract determines whether it’s a safe one.
| Category | Details |
|---|---|
| Topic | Natural Swimming Pools |
| Primary filtration method | Biological filtration via plants, gravel, and microorganisms |
| Main safety concern | E. coli and fecal coliform contamination from wildlife |
| Recommended companies | The Swimming Pond Company, Biotop Natural Pools, Clear Water Revival |
| Typical zones | Swimming zone (deep, plant-free) and regeneration zone (shallow, planted) |
| Risk indicator | Faecal coliforms, enterococci, Pseudomonas aeruginosa |
| Maintenance need | Routine phosphate monitoring and algae control |
| Reference standard | FLL guidelines for natural swimming pools |
| Reference text | How to Build a Natural Swimming Pool by Wolfram Kircher and Andreas Thon |
Let’s start with the obvious tension. Chlorine is a blunt but effective tool used in conventional pools to kill pathogens. Instead, a natural pool depends on oxygen levels, biological processes, plant uptake, and a regeneration zone that works quietly in the background. Three of the four pools tested by researchers examining microbial populations in natural pools had E. coli or enterococci levels above recommended limits, and wildlife was found to be a significant source of fecal contamination. You shouldn’t be alarmed by that. It is a justification for treating engineering seriously as opposed to presuming that nature will act on its own.
Because it contradicts the romantic version of the story, it’s worth pondering that discovery for a while. It sounds adorable when frogs and newts move into your swimming hole, but keep in mind that animals poop in the water they inhabit. The authors of the study pointed out that more research is required before safety standards can be appropriately established because there is a lack of regulation surrounding these systems and the health risks may be higher than in conventional pools. Hoblyn lists leeches as frequent swimmers in his pool, only half-jokingly. When most clients hear that, they subtly change their minds.
The wildlife isn’t actually the greater threat. It’s eco-virtue disguised as complacency. Owners who mistakenly believe that “natural” equates to “harmless” occasionally neglect the unglamorous upkeep that maintains a system’s equilibrium, and that’s when things start to go wrong. algae blooming more quickly than anticipated, phosphate levels gradually rising, and regeneration zones becoming overburdened following a significant downpour. This is not exotic chemistry at all. Wetlands penalize neglect, so it’s more akin to caring for a small wetland.
Strangely enough, there is a useful parallel in the way public health officials discuss regular chlorinated pools. 58% of public pool filter samples tested positive for E. coli, a bacterium usually introduced by swimmers rather than by inadequate chemical treatment, according to a CDC-linked study. In other words, contamination is not specific to natural systems. The simple notion that chlorine equals safety and its absence equals risk is complicated by the fact that swimmers are the primary source of contamination in any pool rather than the water’s inherent filth. In the event that something goes wrong, natural pools simply have fewer chemical backup options.
It appears that design discipline, rather than philosophy, is what distinguishes a truly safe natural pool from a dangerous one. Experts generally advise avoiding swimming in natural bodies of water for a few days following heavy rainfall because runoff can introduce E. coli and other contaminants into natural water sources. This advice applies almost as directly to a poorly buffered backyard pool as it does to a lake. That kind of shock is meant to be absorbed by a well-constructed regeneration zone that is generously sized and planted with the appropriate species. A small one won’t.
No amount of biology can completely eliminate the human element. Since the body can continue to shed parasites long after symptoms go away, public health advice generally advises avoiding any kind of pool natural or chemical for two full weeks following diarrhea. On a hot July afternoon, when the water seems inviting and no one wants to be the one enforcing pool etiquette at a family get-together, it’s easy to forget this rule.
All of this does not imply that natural pools pose a significant risk. It implies that they demand more of their owners. A natural pool requires something more akin to stewardship, whereas a chlorinated pool provides a certain level of assurance check the levels, add the chemical, and be done. Regardless of which system is installed, physical safety barriers, secure covers, and adequate supervision around access are still important, and that aspect of the safety equation never really changes. The biological margin for error is what does change, and Hoblyn and other designers continue to construct them as showrooms instead of persuading people to commit. It’s a good idea. The difficult part is the follow-through.
i) https://www.theguardian.com/lifeandstyle/2015/sep/25/natural-swimming-pools-i-love-mine-but-try-telling-my-clients-that
ii) https://www.filbertpress.com/natural-swimming-pool
iii) https://www.clear-water-revival.com/natural-pool-faqs/
iv) https://urban-water.co.uk/natural-swimming-pools/
v) https://www.fluidra.com/commercial-solutions/inspiration/blog/natural-swimming-pools/