Also known as a bathing pond, the natural pool is becoming more and more popular in the garden, not just for its ecological advantages, but also for its pleasant aspect.
While we see more and more above-ground pools in gardens, an increasing number of people with an organic approach are opting for natural pools. Although fairly new in France, they are extremely popular in Sandinavian countries. These pools don’t pollute, as they don’t require the use of chlorine or other chemical products like algaecides.
A two-part pool
Natural pools are generally built using a waterproof tarpaulin held down with ornamental stones which serve as copings. They can also be made with polyester or concrete. In fact, the material used for a natural pool is of no importance ! What is important is how the pool is managed. It uses the same system of mechanical filtering as is used for normal pools (drainage of the bottom and surface of the pool) as well as a sand-filtering system which eliminates floating particles. It differs from normal pools in the way it treats the water. The water which comes out of the sand filter is separated in two – around 90% of it is directed towards an oxegenizing waterfall to make sure that the water is cleansed, whereas the other 10% is directed towards a natural filtering system.
In this small basin, situated slightly above the big basin, special aquatic plants get rid of the mineral or organic pollution in the water. This system is a closed circuit based on gravitation. The idea is to achieve a slow flow of the water from the big basin so that it passes through the the filtering system at least twice a day.
Here is a list of some interesting plants which filter organic matter effectively and which help their sedimentation : the Mare’s tail (Hippuris vulgaris), the yellow water-lily (Nuphar luthea), the lesser spearwort (Ranunculus flammula), the arrowhead (Sagittaria japonica), and the azollae ferns (Azolla).
When the natural pool is optimized, both basins should function without intervention, just like an organic eco-system.