Goal The first goal is to purify rain water for household and possible consumption. The second goal is to to collect the water again what is used in the household . Rain water collect So lets start and imagine that the water comes directly into the pool. Can we use it for household or for consumption? Directly from the air in normal circumstances it is safe to drink. The pH of rain is about 5,0 to 5,5 . Coffee has a pH of 5. When it comes from the roof it could have toxic chemicals or pollution, pollen or mold. It is not weird to think that you can use it for the household. But we do not use all the water immediately. A part of it we keep in the pool. Standing water could get murky by: - algae; - plankton; - biofilm; - plants. And when that happens, it will be unhealthy for to swim, for household and or consumption. Purify rain water in 3 steps Brief background The most simple way we have seen is a big hole filled with rain water in the backyard and the rain water was transported among 2 meter 2 of reed to purify and it was drinkable (the engineer had also developed the first compost toilet with no water). It was an experiment and only to show how to create drinking water out of rain water and not a project for every day use of the household. But as I have shown, we use much more water in a day for the household than only consumption. It means that we have to reflect on how to use the rain water for household and for consumption. But also to reuse the water what is left of the household or consumption. Steps To purify the rain water we will divide it into 3 parts. In my opinion they are so intertwined with each other that I can´t treat them apart. 1- water circulation; 2- water filter; 3- plants.