The Earthship system of using ...
Published by Tom Mallard, Living Systems, Industrial-Architectural Design
The Earthship system of using collected water has the kitchen and toilet on the septic tank and graywater is used to grow food, this graywater system requires the plants to work properly and any plants will do. Their systems work down to 15cm of rain annually, they do use cisterns and filtration and treatment for collected water purification, their systems are up to code in the USA. However, I realize this is a distributed system and doesn't require sewage piping infrastructure or the need for a separate source of water. For centralized systems, there is no such thing as "cheap" compared to distributed water treatment.