The wetland contains a planting substrate of small gravel into which wetland plants are planted. Water is forced through the plant roots and the substrate which act as a biological filter and physical filter, trapping and breaking down organic matter. The biological filter breaks down complex organic matter into simpler constituent molecules that are then absorbed by the plants in the wetland. Salts in the water are similarly absorbed by the plants. Once a year, usually in winter, the plants are cut back dramatically and the cuttings removed from the pool.

The pool utilises a small pump which ensures a constant flow of water through the wetland. This continuous filtering strips all nutrients, organic matter and salts from the water and gives it its characteristic clarity. The water is totally clear when the pool is working properly, and details can be made out clearly, even at the bottom of the deep end. We have tested the water in pools that are functioning well, and the water is drinking water quality, and tastes really good as it is soft and aerated water.

A stream, waterfall or other form of aeration is essential. The aeration makes oxygen available for the bacteria and micro organisms that are the engine room of the filter.

A wetlandPOOL does contain algae. All surfaces in the pool develop what is referred to as a 'patina of algae' which gives the pool its characteristic golden colour. In the first year, there can be quite a lot of algae growth, but with time the growth drops off dramatically.

A weir removes leaves and other debris that fall into the pool. Water currents flow up through the swimming area to prevent leaves from sinking and assist the weir.

Water flow is designed to ensure no pockets of static or stagnant water, which prevents mosquito larvae from establishing and ensures that all the water is oxygenated, clean and fresh, just like a mountain stream.