Natural Pools: Dragonflies at the deep end

It was an idyllic, English country garden, set in acres of rolling farmland. Snowdrops nestled at the creaky old gate, through which we crept, enchanted, into a grove of apple trees and on towards a lush green lawn. A Robin fluttered past us and perched proudly atop a cherry tree, scattering a confetti of pale pink blossom into a totally hideous artificial-blue rectangle.

The swimming pool was as out-of-place in this bucolic setting as a satellite dish stuck on the side of a medieval castle. A synthetic stink of chlorine rose from beneath the scum of mouldering petals to pollute the fresh morning air. "Ta daaa!" trumpeted the optimistic estate agent, whose aftershave was vying for nasal attention with the chlorine. "An established country garden and a pool! And this one is quite a bit cheaper than some of the other places you've looked at." Well, no wonder, with this monstrosity in it. I like to swim. But I prefer a natural view. And like so many other potential buyers before us, we walked briskly away.

But there is another option for those facing a similar dilemma. Traditional swimming pools can now be converted into natural swimming ponds designed to blend organically into their surroundings and requiring no nasty chemicals to keep them clean. Natural swimming ponds first gained popularity in Germany in the late 1980s and quickly spread across the Continent. They were introduced to Britain in 2001 and now there are several companies offering to install a swimming pond from scratch, or convert an old eyesore into a dreamy space out of a Monet painting.

They certainly look nice, but do they work without turning into stagnant, mosquito-breeding swamps? "Swimming pools are essentially isolated eco-systems," explains David Nettleton of Clear Water Revival, who worked as an aquatic ecologist and water treatment engineer for aquariums before moving into the "swimming pond" business. "The basic philosophy behind water quality in a conventional swimming pool is to kill everything short of the swimmer. But in a natural swimming pool we harness nature's own processes to produce clean, clear water." So where school pools used chlorine to exterminate "nutrients" that fall into them (like leaves, soil and skin) a natural pool uses a filter of "friendly bacteria" to break these down organically.

To build such a self-sustaining ecosystem, most pools will need two zones: a swimming zone and a planted or "regeneration" zone with a base of gravel made up of a mix of rocks and minerals to nourish the plants.

In most conversion cases, the edge of the existing pool is lowered and a new shallow section is installed around the edge for the regeneration zone which is then covered in gravel and planted with flora of the client's choosing. Designers can either put in plants to encourage wildlife – for those who want to splash about in the company of frogs and dragonflies, although mucky fish are an unwise addition – or create a less inviting environment for those who prefer to swim unaccompanied by the local fauna. A new swimming pond should take around two months for its ecosystem to stabilise.

A pump is used to keep the water moving through the filtering area of the regeneration zone. And surprisingly, some pools will also stand being heated up to 28C. Those wishing to be extra environmental can achieve this with solar heating, as well as maximising the sun's effects by lining the pool with darker colours. Cleanliness of the swimming area can be maintained in the traditional way, by skimming with a net, or using a robot. Nettleton claims that maintenance costs for a natural pool are about a quarter of those associated with normal swimming pools. Tim Evans, managing director of gartenART, has installed over 40 natural swimming ponds since 2003. He says the maintenance is also much more enjoyable: "it's essentially gardening – and much more relaxing and rewarding than having to muck about measuring out chemicals".

Richard Locke, 42, and his wife Mary bought their beautiful 16th century home in Kent two years ago. "The house came with a rather derelict 1970s swimming pool, about 30 ft by 15ft," he says, "surrounded by nasty concrete tiles. It didn't really fit the surroundings." He hired gartenART to convert the old pool into a natural pond. "I know many of the natural pools have more organic shapes, but we stayed with the original, formal rectangle because it was in keeping with the arts and crafts style of the house. Like a traditional lily pond." Locke had been attracted to the concept on aesthetic and environmental grounds, but was "unprepared for how different it feels to swim in fresh water – it's much softer and cleaner than chemically-treated water. It's fantastic. We have newts now, which is apparently a good sign". The Lockes' children love playing in it while their parents relax on the stone terrace on summer evenings. There's a modern English country scene that wouldn't have potential buyers legging it.

Natural pools: A buyer's guide

* Natural pools shouldn't cost more than traditional pools, says David Nettleton of Clear Water Revival. "From scratch," he says, "you're looking at around £40,000 to £120,000 for a typical bespoke family pool."

* Because they don't use expensive chemicals, general maintenance costs are roughly 25 per cent of those associated with traditional pools.

* Design is flexible. Depth in the swimming zone should be between 1.2 to 2.2m. You can choose your own aquatic flora and fauna although fish are not recommended.