Water Cycle
Water systems in the home and landscape are integral and create a simple, efficient, on-site water management system. The project promotes ecological principles and the larger water-use framework of the TVA offers alternatives to centralized systems introduced here in the 1930s. The project combines centralized and decentralized systems, with numerous safe-guards to ensure safety and redundancy.
Excluding roof area the site is 99% permeable; furthermore, roof water is collected and used in the home and landscape. Rainwater from the roof (930 sf) is stored in a cistern (400 gallons) located in the home’s mechanical room. Rainwater is treated with UV and carbon filtration for non-potable use in the home (toilet, clothes washing, hose bibbs). A full cistern overflows to a second cistern (200 gallons) for irrigating vegetable beds; this cistern in turn overflows to the second bio-retention bed entering a forebay to slow water flow and velocity. Water flows through the beds via gravity, low-flow channels and overflow points until it reaches the lowest bed. Each bed will hold water from a 2.5” rain event (very significant storm) before overflowing from the lowest bed into the existing forest swale. Grey water from the home is discharged below ground to the top-most bed for treatment and infiltration.
One year of post-occupancy evaluation has revealed that the home is able to collect and treat rainwater that is safe for human contact by EPA Human Health Criteria. In the first year of study, 39,388 gallons of water has been passively returned to the landscape through greywater and rainwater overflow systems. Potable water is only used for landscape irrigation in cases of an empty cistern and to establish the landscape in the first year of planting. Only 2,379 gallons of potable water was delivered to the landscape— a 96.6% reduction from typical US use (defined in the 1999 AWWA “Residential End Uses of Water” Report). This volume of necessary irrigation is anticipated to drop significantly further (85%+) in the second year of study, even as the landscape flourishes. Over 73% of waste water has been reused on-site.
Metrics
Percent reduction of regulated potable water:
62%
Is potable water used for irrigation:
No
Percent of rainwater from maximum anticipated 24 hour, 2-year storm event that can be managed onsite:
85%