A natural bathing pool installed by Austrian specialist Biotop near Merano in Italy

One day recently I was enjoying a swim in a natural freshwater lake among coots, moorhens and pink and white water-lilies when I suddenly discovered that I had a swimming companion – a vast, seedy-looking pike. This kind of thing is a common problem in natural bathing but the answer might lie in freshwater swimming pools that are being revolutionised by chemical-free water filters.

Natural pools that are kept clean by the movement of water through aquatic plants such as reeds first appeared in Europe in the 1980s. They looked more like garden ponds or small lakes than conventional pools and had a limited season because they could not be heated.

Today’s freshwater pools can be heated and no longer require plants to keep them clean. These are two of the factors that have spawned a growing number of natural public pools in continental Europe. In the US, where freshwater swimming pools are still a novelty, a 1,600 sq metre freshwater pool has just been completed for a private client on Nantucket Island by New York landscape architects James Corner Field Operations and Biotop, an Austrian company that, along with several other companies in Europe, has been one of the pioneers of freshwater bathing facilities.

While such pools are expensive (the owner of the Nantucket pool declined to reveal the price), initial capital investment is offset by lower running costs compared with conventional pools.

“Building costs are about 20 per cent more than a conventional pool but the running costs are about 50 per cent lower,” says Will Woodhouse of Woodhouse Landscape, the main UK agent for Biotop.

“In the new system, a biological sand filter breaks down organic matter, which can be anything from bird droppings to insects,” says Woodhouse. “Then the water goes through Biotop’s patented non-chemical filter, which removes all phosphorous. This creates such clean water that nothing can grow in it.”

The fact that planting need not be part of the design also frees up space. Until now half the area of a pool had to be given over to cleansing aquatic planting. Even so, most people choose to include decorative flora.

“Most people still want a garden swimming pool with some plants and the odd dragonfly flying past,” says Woodhouse. “The new system can be combined with plants for nature-lovers and also put indoors and heated – alternative options for our cooler climate.”

However, fish are out of the question, and when decorative plants are included a maximum temperature of 26°C is recommended.

Such pools are also low-maintenance. A “self-skimmer” of constantly circulating water removes leaves or insects and a surface vacuum cleaner removes dust. The skimmer has to be emptied every few weeks and, in plant-based systems, plant fertiliser has to be added. Otherwise minimal upkeep is required.

The technology behind plant-free freshwater pools varies from company to company and the precise details of filter specifications are a closely guarded secret.

Tim Evans, managing director of natural pool design and construction company Gartenart, is typically non-specific. “The water is purified using minerals and plants,” says Evans, who has installed about 40 freshwater pools to date. “The main principle is to keep nutrient levels low so that algae don’t grow. We filter the water through chippings such as granite. Why would anyone use chemicals if you can do this?”

One of Gartenart’s recent projects was a 30 sq metre freshwater pool at Foxhills Country Club in Surrey. It cost about £45,000 and operates on a filtration system rather than depending on plants. It looks like a conventional rectangular pool but includes minimal marginal planting at one end for decoration and can be heated up to 26°C. So far it has not required maintenance since its installation last November.

The new breed of freshwater filter systems makes converting old pools easy because there is no need to double the size of the pool to accommodate aquatic plants.

Woodhouse says a growing number of clients are enquiring about derelict pool conversions. After my pike experience I hope his client list includes some of my friends.

www.gartenart.co.uk
www.woodhouselandscape.co.uk
www.biotop-natural-pool.com

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Garden gear: Summer houses

While England’s green and pleasant land was bowing to the industrial revolution, a 19th-century mill owner in Cheshire, north-west England, created a garden representing John Bunyan’s Christian allegory The Pilgrim’s Progress, complete with a revolving summer house bearing the inscription: “Bethel – House of God”.

Today anything that captures the sun’s rays seems godly and Norton Garden Structures can make revolving buildings of any symmetrical design, with square and octagonal summer houses proving popular. Prices start at £10,925 for a 3 sq metre rectangular pavilion. This, like all prices quoted below, does not include the required concrete base.

Ornate Garden makes a revolving summer house made of steel, wood and polycarbonate. The interior includes a dining table, 12-volt electrics and seating for 14, so the £15,000 cost works out at just over £1,000 per guest.

Garden Sun Studio’s Pygmalion (right) is a pentangular 6 sq metre revolving building in wood with a felt roof. It costs £8,000.

Those who want a chunk of history should scour auction and salvage houses. As I write, Symonds Salvage is offering a restored 7ft 6in x 7ft 6in Victorian revolving summer house for £4,500. Hardly a house of God, but it is charming.

www.nortongardenstructures.co.uk
www.ornategarden.com
www.gardensunstudio.com
www.symondssalvage.co.uk