Zero Water Part 3: A sustainable concept for water in the Texas Hill Country

Part 3: “Right-sizing” the RWH system is key to sustainability

 

There is a caveat on the “zero” in Zero Net Water. The cistern in a building-scale rainwater harvesting (RWH) system operates in the same manner as a reservoir in a conventional surface water supply system – it stores the water for future use. Just like a reservoir, a building-scale cistern has a “firm yield” that will cover a given water demand profile. The building-scale cistern is typically sized to cover most conditions, with it being presumed that imported backup supply would be added to get through the worst drought periods. Considerations of cost efficiency and the sustainability of the backup supply system lead to the concept of “right-sizing” the system. This is the combination of roofprint and cistern volume relative to the expected water usage profile that would result in only limited backup supply requirements, needed only during the worst drought periods.