A natural swimming pool is a concept that's becoming more popular in the UK. A relaxing dip in your own pool, in your own garden is an idea that appeals to many. Chemicals are not used to clean the water; instead natural swimming pools are filtered using aquatic plants, which clean the water naturally.
Whether you're constructing a self build and looking to add a natural swimming pool as part of your landscaping or you're looking to add a pool to your existing plot as part of an eco-friendly wildlife garden, here's all you need to know about options, designs and costs.
Types & Benefits
What Types of Natural Swimming Pool Are There?
Natural swimming pools – which can be as small as 15m2 – come in two main forms: the traditional natural pool (or pond), and the living pool, which visually looks more like a traditional filtered pool.
Benefits of a Natural Swimming Pool
- No chemicals — A fresh water pool with no chemical disinfectants is good for swimmers’ skin and the environment.
- A pond and pool — A natural swimming pool looks just like a pond and is as natural as they come.
- No one-size-fits-all — A living pool is a great alternative if space is limited or if you’d prefer a more traditional-looking pool.
- Low maintenance — With only a little pruning needed, the plants keep a natural pool clean and the filter systems in a living pool keep it debris and algae-free.
- A haven for wildlife — a natural pool will of course invite a whole host of wildlife into your garden.
How it Works
How Does Filtration Work in a Natural Swimming Pool?
With a natural swimming pool, the idea is that a large, deep pool – the swimming area – is surrounded by marginal planting that filters and purifies the water naturally. In essence, this type of natural swimming pool has the look and feel of a large pond.
Construction involves creating a reinforced, lined swimming pool area, alongside a series of filtration beds made again with a liner and a series of planted shingle pools, which help to remove debris.
Unlike a traditional pool, a natural swimming pool’s feel is best maintained by dark green liners. As its filtration system relies entirely on plants using a darker liner will give some secondary warming that the light blue or aqua liners of a traditional pool don’t. You can also install lighting both in the main swimming area and through the marginal filtration beds.
Designing a Natural Swimming Pool
Choosing a Shape For a Natural Swimming Pool
The swimming area of the natural pool can be informal in shape or more rectangular. A natural swimming pool can take up quite a bit of space and like any pool, needs to be constructed on a level or levelled site.
For a pool with a swimmable area of 20m2 the entire pool would need to be 40m2. This kind of size suits rural locations and those with larger gardens because alongside the pool you will need shallow space for a deck, terrace or jetty access point. The pool area will also need to be planted to merge with the herbaceous and shrub planting that outline the margins of the pool.
How to Zone a Natural Swimming Pool
Often the two zones, the swimming pool and the filter beds, are separated by a shallow band of stone. This separation can be given a natural feel, or a more contemporary one (using a band of cut stone, for example).
Either way, this band stops the soil of the planted filtration beds moving into the main body of the pool. It is usually positioned roughly 50mm below the surface and should be 100mm to 200mm in width.
One of the advantages of a natural pool is the shallow planted margins that form its natural filters. Rather than the traditional drop into water, the margins on natural swimming pools are sloped.
A 20m2 pool, for example, will slope downwards about a metre from the edge to roughly 400mm below ground level (or your set 0 point if you’re building on a slope and are creating an artificial level). The depth of the swimming area will be around 1.5m. So for a 40m2 pool the shallow graded margins need to be 20m2 — this will include 7m2 of bio (plant-based) filtration and 13m2 of marginally planted space that will allow the water to purify.
The swimming area will be 20m2 with a depth of at least 1.5m to allow good swimming and stop plants creeping away from the ledges to the swimming area.
How to Plant a Natural Swimming Pool
Planting for a natural pool is key. Of course, like any part of the garden, it will require maintenance — herbaceous aquatic plants will need to be recut back in the late autumn.
It’s also worth remembering that the term ‘filtration plants’ can be a misleading one as the plants do not remove particulate matter from the water. What they actually do is absorb and capture nutrients from the water — in turn meaning algae (which thrive on these nutrients) will not grow and bloom in the water.
The amount of nutrients that a plant absorbs is more or less proportional to the amount of plant growth. So, plants that grow ‘greener’ are removing more nutrients, but this can also mean that they grow more aggressively.
Common species used to filter include marsh marigold, flag iris, loosestrife, hop sedge, water mint and water lilies.
Fresh water attracts a host of acrobatic insects. Old-world creatures such as damselfly feed on mosquito larvae, using leggy stems of flag iris to emerge from the water for their flirtatious flights. Pond skaters, water boatmen and iridescent dragonfly are common. Surprisingly for their size, many aquatic species depend on freshwater ponds for refuge, including more than 100 UK Biodiversity Action Plan priority species.
How Much Does it Cost to Build a Natural Swimming Pool?
A natural swimming pool costs from £300 to £600/m2, with the price /m2 decreasing as the overall area increases. This may sound odd, but as the pool gets bigger many of the expensive items it requires – machinery hire, waste disposal, and some materials – remain the same in terms of up front cost. These items are then used over a larger volume of space, with the result that it effectively costs less.
Added to this, smaller natural swimming pools are often located in more restrictive spaces, which has an impact on costs and labour. Designs are landscaped to sites and individual requirements, so construction costs may be high compared with traditional pools. Over time, however, natural pond owners save on the cost of chemicals and expensive filtration equipment.
Natural Living Pools
What is a Natural Living Pool?
Alongside the natural pool and its marginal planting, Biotop – a specialist company that has been making natural pools for over 30 years – has introduced a natural filtering system that works to create a more traditional-looking swimming pool.
For homes where space is limited or perhaps where a more contemporary look is desired, the natural living pool has a filter system that scoops the water away through a curved filter to remove debris.
It also includes a series of hidden underground sand filters for cleaning before pumping the water back into the pool. This removes the phosphorus that is the main cause of algae blooms. Lighting can be added into the main body of the pool.
How Much Does a Natural Living Pool Cost to Build?
This system is expensive and really has to be installed by a qualified specialist. Expect an average-sized 20m2 pool to cost in the region of £60,000.
Finding a Natural Swimming Pool Specialist
There are a number of specialist companies in the UK. Choose one that is highly recommended, such as Big Fish Landscapes or Water Artisans, both of which have the accolades of RHS Chelsea Gold Medals and international associations with natural pool technicians. Ask to have a consultation about your site, and to talk through what natural pool you would like.
(MORE: Swimming Pool Guide)
Paul is an award-winning landscape designer, based in the Cotswolds.
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