The first time I swam in a natural swimming pool, I was seven years old and had no idea I was experiencing something revolutionary. It was at my great-aunt Margaret’s rambling country property in Devon, and to my young eyes, it just looked like a very fancy pond you were allowed to swim in. I remember the shocking clarity of the water, the tickle of tiny minnows around my ankles, and my mother’s constant warnings not to disturb the plants because “they’re working very hard to keep the water clean.”
It wasn’t until decades later, when I found myself standing beside that same swimming pond as an adult, that I truly appreciated what Aunt Margaret had created back in the 1980s when most of Britain was still firmly committed to chlorinated blue rectangles. She had somehow intuited (or more likely, read about in one of her obscure German gardening magazines) the principles of biological filtration that are now becoming mainstream in natural pool design.
“Your aunt was always ahead of her time,” my mother said, as we watched bees visiting the yellow flag irises growing along the pool’s edge. “Everyone thought she was barmy when she put this in. The neighbors were certain we’d all die of some horrible water-borne disease.” She laughed. “Forty years later, and the only thing anyone’s caught from this pool is an appreciation for dragonflies.”
That conversation reignited my childhood fascination with Aunt Margaret’s swimming pond and sent me into a research deep-dive on natural swimming pools. I’ve since visited dozens of these chemical-free swimming spaces across Europe, interviewed several designers and builders, and—I’ll admit with only mild embarrassment—created a detailed 3D design for my own future natural pool, despite currently living in a second-floor flat with access to only a communal garden where I’m fairly certain the residents’ association would not approve of my converting the lawn into a swimming ecosystem.
For the uninitiated, natural swimming pools (sometimes called swimming ponds) are water features designed for swimming that maintain clean, clear water without chemical disinfectants like chlorine. Instead, they rely on biological processes similar to those in natural freshwater ecosystems to purify the water. They typically include a swimming area and a separate regeneration zone filled with carefully selected aquatic plants and beneficial microorganisms that filter and clean the water naturally.
The science behind this approach is fascinating and surprisingly straightforward once you understand the basic principles. In essence, natural pools recreate the same purification processes that keep healthy natural bodies of water clean. The key elements include:
Physical filtration, where particulate matter is trapped by substrate materials and plant roots.
Biological filtration, where beneficial bacteria break down potentially harmful organic compounds.
Nutrient competition, where plants in the regeneration zone consume nutrients that might otherwise feed algae.
UV sterilization, either from natural sunlight or supplemental systems, which helps control certain microorganisms.
The result, when properly designed and maintained, is water that’s clear, clean, and safe for swimming without the chemical cocktail of conventional pools. No red eyes, no chemical smell, no worrying about what those pool chemicals might be doing to your skin or the environment when they’re eventually backwashed into the water system.
There are several approaches to natural pool design, ranging from the purely biological to hybrid systems. The original European designs, like Aunt Margaret’s, rely almost exclusively on plants and beneficial microorganisms for filtration. These typically feature a swimming area equal in size to the regeneration zone—essentially half pool, half planted pond.
Modern designs have evolved to include more mechanical components like pumps and skimmers to aid circulation, specialized filter media to host beneficial bacteria, and sometimes even controlled UV systems to provide additional sterilization. These advances allow for smaller regeneration zones (sometimes as little as 30% of the total water surface) and more flexibility in design aesthetics.
After visiting a particularly stunning natural pool in Cornwall last summer, I cornered the owner, a landscape architect named Julian, and bombarded him with questions about the construction process. Poor Julian probably regretted mentioning his pool to me at what was supposed to be a casual garden party, but he graciously walked me through the key elements that make these systems work.
The structure of a natural pool typically includes the swimming zone with vertical or steeply sloped sides and a flat bottom for safety, separated from the regeneration zone by a submerged wall that allows water to circulate between the two areas but keeps swimmers out of the delicate plant ecosystem. The entire system is made watertight using either a flexible liner (typically EPDM or reinforced PVC) or built as a concrete structure sealed with a non-toxic waterproofing system.
“The most critical factor,” Julian explained as we peered into his crystalline water, “is getting the water circulation right. You need to ensure there’s constant gentle movement pushing surface water from the swimming area into the regeneration zone and then drawing the clean, filtered water back into the swimming area from the bottom.”
This circulation is typically achieved using low-energy pumps that consume far less electricity than conventional pool systems. Some purist designs like Aunt Margaret’s rely on strategic placement of the regeneration zone to create natural thermosiphon circulation, though most modern installations include some mechanical assistance to ensure consistent water quality.
The heart of any natural pool is the regeneration zone—the aquatic garden that does the actual water purification work. Plant selection for this area requires careful consideration of local conditions, water depths, and specific filtering capabilities. In the UK climate, reliable performers include:
Marginal plants like yellow flag iris (Iris pseudacorus), water mint (Mentha aquatica), and marsh marigold (Caltha palustris), which thrive in shallow water around the edges.
Emergent plants such as reeds and rushes, whose extensive root systems provide crucial surface area for beneficial bacteria.
Submergent oxygenators like hornwort (Ceratophyllum demersum) and water milfoil (Myriophyllum spicatum), which release oxygen into the water and help control algae.
Floating plants like water lilies, which shade the water surface and help prevent excessive algae growth.
After visiting Julian’s pool, I became slightly obsessed with the plant selection process, creating elaborate spreadsheets comparing different aquatic plants’ filtration capabilities, root depth, flowering periods, and winter hardiness. My friend Sasha, upon seeing these documents, suggested I might be overthinking things slightly. “It’s a pool, Eliza, not a PhD thesis,” she said, though she later admitted the resulting plant combinations I’d designed would probably be quite beautiful.
Beyond the plants themselves, the substrate in which they grow plays a crucial role in water purification. Most natural pools use carefully selected gravels and aggregates that provide both physical filtration and vast surface area for beneficial bacteria to colonize. Some systems incorporate specialized mineral media like zeolite, which has exceptional capacity to bind ammonium and other potential pollutants.
The water quality in a well-designed natural pool is remarkable—clear enough to see a coin on the bottom at two meters depth, yet teeming with microscopic life that creates a balanced, self-regulating ecosystem. This isn’t the sterile environment of a chlorinated pool but rather a living system where various organisms keep each other in check.
“The key difference in maintenance,” Julian explained as we watched dragonflies skimming across his pool surface, “is that you’re working with biological processes rather than fighting against them. Instead of constantly killing everything in the water with chemicals, you’re nurturing the right balance of life.”
This shift in perspective leads to different maintenance requirements. Conventional pools need regular chemical testing and adjustment, shocking, and algaecide treatments. Natural pools instead require occasional plant trimming, removal of fallen leaves and debris, and monitoring the overall ecosystem health.
Many new natural pool owners worry about mosquitoes, but a properly designed system actually controls them better than many conventional pools. The movement of the water prevents mosquito larvae from developing, and the complex ecosystem includes numerous predators that feed on any larvae that might appear. In Aunt Margaret’s pool, a healthy population of pond skaters and dragonfly nymphs keeps potential pest insects firmly in check.
The seasonal rhythm of a natural pool follows a more natural pattern than conventional pools, which can be jarring for those accustomed to chemical systems. In spring, there might be a brief period of green water as the ecosystem rebalances after winter dormancy. Summer typically brings crystal clear conditions when the plants are at their most active. Autumn requires attention to falling leaves, while winter sees the system slowing down but remaining fundamentally stable beneath the surface.
When I asked Julian about the challenges of his natural pool, he mentioned the learning curve. “It’s like getting to know a living thing rather than operating a machine,” he said. “There’s a period where you’re learning to read the signals—what certain plants are telling you about water conditions, what changes in clarity might mean, how the system responds to heavy rain or hot weather.”
This responsive relationship with the pool ecosystem is something every natural pool owner I’ve spoken with mentions. Sarah, who installed a natural pool in her Gloucestershire garden three years ago, described the shift in how her family interacts with their swimming space: “With our old chlorine pool, it was just somewhere to swim. With this, we find ourselves visiting it even when we’re not swimming—watching the wildlife, checking how the plants are doing. It’s become the focal point of the garden in a way the old pool never was.”
The wildlife factor is indeed significant. Within months of completion, natural pools typically attract an astonishing array of creatures—damselflies and dragonflies, water beetles, amphibians, birds that come to drink and bathe. Sarah’s children have become amateur naturalists, keeping journals of the species they observe at their pool. “They learn more biology here than they ever would from a textbook,” she noted.
Of course, sharing your swimming space with wildlife raises questions for some potential owners. “But what about the frogs?” is perhaps the most common concern I hear when discussing natural pools. Most owners report that wildlife primarily stays in the planted regeneration zones rather than the swimming area, though occasional encounters do happen. As one owner memorably told me, “Yes, sometimes a frog might join you for a swim. I consider it a feature, not a bug—though technically, I suppose, it’s neither.”
From a practical perspective, natural pools can be created in almost any size, though most designers recommend a minimum total water surface of about 30 square meters to maintain stable ecosystem function. The swimming zone should be at least 2.5 meters wide for comfortable swimming, with a depth of 1.2 to 2.2 meters for safety and thermal stability. Smaller systems are possible but will typically require more technical support like additional filtration to maintain water quality.
Cost is inevitably a consideration. For a professionally designed and installed system, natural pools typically cost 10-20% more upfront than a conventional pool of equivalent size. However, the ongoing maintenance costs are substantially lower—no chemicals to purchase, lower energy usage for pumping and filtering, and no need to fully drain and refill the pool periodically.
“The economics made sense for us even before considering the environmental benefits,” Julian explained. “We estimated our natural pool would break even with a conventional system within about seven years, just on maintenance savings. Everything after that is effectively money in our pocket.”
The environmental advantages extend beyond chemical avoidance. Natural pools create valuable habitat in our increasingly fragmented landscape, supporting pollinators and other wildlife. They use significantly less energy than conventional pools—as little as 5-10% of the electricity needed for standard filtration and pump systems. And because they don’t require draining and refilling, they conserve water, particularly in drought-prone regions.
For homes with limited space or specific aesthetic preferences, hybrid systems offer an interesting middle ground. These incorporate some biological filtration elements while maintaining a more traditional pool appearance. Constructed wetland filters can be designed as attractive garden features separate from the swimming area, or hidden entirely in technical chambers, providing natural purification without the pond-like aesthetic.
A particularly intriguing development is the conversion of existing conventional pools to natural systems. I visited a remarkable example in Sussex last year, where a family had transformed their 1980s rectangular chlorine pool into a natural system by adding a regeneration zone along one long edge and installing the appropriate circulation and filtration components. “We kept about 70% of the original structure,” the owner told me, “which saved substantially on construction costs while giving us all the benefits of a natural system.”
After all my research and site visits, I’ve become thoroughly convinced that natural pools represent the future of private swimming. They align environmental responsibility with practical benefits—clean, gentle water that’s kind to skin and eyes, lower running costs, reduced maintenance time, and the creation of beautiful, biodiverse spaces that enhance rather than detract from garden ecosystems.
I’ve also realized that my great-aunt Margaret was far more visionary than any of us gave her credit for. Her swimming pond, now nearing its fourth decade, continues to function beautifully with minimal intervention—a testament to the resilience and sustainability of well-designed biological systems.
Last summer, I helped her clear some encroaching vegetation from the regeneration zone, carefully wading among marsh marigolds and water forget-me-nots. “You know,” she said, pausing to identify a water beetle skimming across the surface, “when I first put this in, people thought it was just another of my eccentric projects. Now the neighbors are all asking for advice on building their own.” She smiled with the quiet satisfaction of someone whose eccentricity has been vindicated by time.
“Do you think you’ll ever build one?” she asked as we sat dangling our feet in the cool, clear water afterward.
I described my elaborate design plans and spreadsheets of plant selections, making her laugh. “So exactly where are you planning to put this masterpiece? On your balcony?”
“Someday,” I promised, watching dragonflies perform aerial acrobatics above the water lilies. “When I have the space, this is exactly what I’ll build.”
Until then, I’ll continue my enthusiastic evangelism for natural swimming pools, collecting design ideas, visiting examples, and yes, maintaining my possibly excessive spreadsheets of aquatic plant filtration capabilities. Because once you’ve experienced the alive, vibrant quality of swimming in water purified by living systems rather than chemicals, chlorinated pools feel like a relic from a less enlightened time—a time when we believed the only way to create safe water was to kill everything in it, rather than nurturing the right balance of life.
