Once the water runs down the drain, everything changes. The bulk of water treatment is carried on indoors so that the system can work year-round. A filter strains out grease and particles. The planter itself is 2.5 feet deep and filled with topsoil over pumice. Bacteria in the pumice eat bacteria in the water and help clean it up.
Plant roots grow into the pumice, where they act as filters and oxygenators.
It is not drinkable. On the south side of the Nautilus, close to the house where it can collect and retain warmth, is a septic tank similar to a conventional tank except that it has a trombe wall or solar face to heat and encourage the anaerobic process. Like the graywater planter, the cells are filled with soil over pumice, and bacteria and the roots of indigenous plants growing in the cells act upon the water. The system gives the option to go conventional, but also of totally containing its sewage. In Colorado, code says that the septic tank can't be closer to the house than 5 feet, and the leach field can't be more than 20 feet away from the house.