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What is a natural swimming pond or pool
For ease of understanding, this diagram is not necessarily in proportion and only includes the basics. Items such as external bio filiters, pre filters and waterfalls are not shown. Please hover your mouse over the key areas of the diagram for more information.
The outdoor swimming pool has never really worked in the UK climate, after all you get nothing but maintenance for the odd day of sunshine. And to top it all, a pool does nothing for the value of your property. So what’s different about a natural swimming pool or as they are often referred to, natural swimming pond?
A swimming pond is a creation that uses nature and if designed well, enhances and settles into the garden landscape. This is not a bright blue rectangular concrete hole in the ground, with that familiar smell of chemicals. The swimming pond is a natural environment, an oasis for microorganisms, plants and insects that all form part of the ecosystem, resulting in a crystal clear pool that when the sun does shine, is there to be enjoyed by man as well.
We have been swimming in rivers, lakes and ponds since the beginning of time and the big difference today is that we want to enjoy the water without catching something unpleasant. That’s why chemical systems were developed for pools and their effectiveness is often described as ‘killing everything but the swimmer’.
The concept of using natural systems to clean the water is quite recent, dating back to the mid 70’s in Austria where the green shoots of the environmental movement wanted a better swimming experience. Since then, many swimming ponds have been built on the continent, not only for private use but large public ponds as well. They say the water is good enough to drink once it is returned to the pool. In the UK the history is much shorter. The first private natural swimming pool was constructed in 2001 and estimates are of 25 pools now built in the with a number currently in construction.
How does it work?
The concept is covered in more detail on another page but the idea is to create a swimming zone within a pond. This zone will be deep and large enough for your swimming needs. Around the swimming zone is the planted regeneration zone. A retaining wall between these two areas keeps them apart. The retaining wall tends to finish about 300mm below the water surface so that water can flow freely from the swimming zone to the filter zone. From a visual perspective, this allows the swimming zone to merge into the overall feel of the pond.
The pond is lined and the regeneration zone outside the swimming area filled with suitable aggregate which allows bacteria plenty of surface area to cling too. Don’t be concerned about bacteria as they are essential, performing the task of cleaning the water. A variety of bacteria decompose any organic matter releasing nitrates and phosphates. Above the aggregates, plants not only feed on these nitrates and phosphates, but also transform the pool in to a natural pond nestling in its environment. Plants range from those that prefer deeper water such as lilies to those living in the margins and bog areas. Perforated pipes beneath the regeneration zone allow cleaned water to be drawn by a pump and returned to the swimming zone. Other components in the plumbing system includes skimmers for removing leaves and large debris, filters for finer particles and UV filters for added security.
The bacteria that do the work in the regeneration zone are aerobic so need oxygen. The plants help channel oxygen via their root systems but additional aeration is always a plus and can be built into a feature such as a waterfall or fountain. As a rule of thumb, the filter area should be as large as the swimming zone. If your space is critical, or the design does not allow for the filter area then biofilters are available. These are boxes filled with a mesh material into which you introduce the bacteria. The water then passes though the filter and is cleaned. Don’t forget though, if you are trying to achieve the look of a natural pond, then you need plenty of space devoted to the regeneration zone to achieve the desired effect.
The design of ponds can be varied. What is described above is the basic concept but the only controlling factor is one’s imagination. A natural swimming pond can be very modern and minimalist. The swimming zone can be separate to the regeneration zone - the possibilities are endless.
The skimmer collects large debris such as leaves and twigs using a strainer plate. Finer debris (less than 5mm) such as dust, grit and hair are then removed by the filter pad within the strainer unit.
The skimmer is fitted in a position where surface debris would normally be blown by the prevailing wind. It is connected to the suction side of the pump
The basic pond consists of two zones (Swimming and regeneration) separated by a wall. The regeneration zone should be 50% of the surface area.
In our basic pond the swimming zone is the central area. This is usually 2m deep in its deepest area which allows for shallow dives. This area also needs shallow surfaces for standing. Clean water from the pump is discharged into the bottom of the swimming zone to ensure good circulation and to prevent build up of silts on the bottom.
The separating wall is approximately 1m high and keeps the two zones separate. The wall can be constructed in a variety of ways including concrete block, timber or plastic panels. The water surface is 300mm above the separation wall which reduces the visual impact of the wall and allows for water to be drawn from the swimming zone to the regeneration zone.
The regeneration zone is where the cleaning takes place using bacteria and plants. In the bottom of the zone. Perforated drainage pipes connected to the suction side of the pump, draw water through the filter bed. This bed can be made of many materials providing they a pH neutral and give plenty of surface area for bacteria to colonize. Gravels can be used but material such as expanded clay or pumice (lava rock) with their open structure are much more effective. The Bacteria transform the waste materials into nitrates which the plants use to grow.
Keeping The Water In
A liner is used to seal the swimming pond along with an underlay to provent te risk of piercing. The liner must be free from chemicals that could harm the natural eco system or the swimmers. We recommend natural rubber and epdm liners as they offer both flexibility and strength. Liners come with guarantees of 20 years +
The pump is the heart of the system. During summer months it must circulate the water 4 times every day. Pump efficiency is extremely important to keep running costs down. Mountain Pools only use high efficiency pumps so you don’t need to worry.
We always recommend using UV filters as a precaution in the plumbing circuit to ensure the water quality entering the pool is spot on.