Filtering types In the book I read, there are 4 filter types: - Hydro Botanical Systems (HBS); - Technical Wetland (TWL); - Biofilm-accumulating Substrate Filter beds (BSF); - Additional filtering, pre-filtering and water treatment units. I will concentrate on the first three items. The fourth is also among others with chemicals. I only mention shortly the filter types. In a later chapter I will more explain with draws and comment. The 3 filter types, HBS, TWL and BSF have their own function of filtering, own flow rate and own type of plants. If you only use HBS it means that 65% of the total surface has to be planted. With the combination of three, HBS TWL & BSF, it is between 5 and 20%. The location with the filter types is called regeneration area and the swimming pool is called the swimming area. There is also an order of the filter types. The last in the chain is HBS. For the first I choose BSF because of the highest flow rate and there are no plants so if it rains it does not ruin plants. HBS has a flow rate of < 0,2 m/hr, and dense planting, TWL has a percolation rate of < 0,3 m/hr, densely planted, BSF has a percolation rate of >>0,5 m/hr, 24/7 movement, plants only for decoration. The swimming area should be at least 3 x 6 m 2 with a dept at least 1,8 m. Better is 2 m to 2,5 m for less stirring up the sediment. Content swimming pool We also want to use the swimming area for household. The swimming pool has a content of 3 x 6 x 1,8 m, gives 32,4 m 3 (is 32.400 liters) if we we use the figures of the previous chapter. Is it sufficient? challenge calculation To calculate the size of the swimming area you have to find out the influence of the next subjects: - rainfall; - roof surface; - evaporation; - household use - garden botanica - buffer.