Dwell Design Conference – Greywater
In June, I made a presentation at the Dwell Design Conference in Los Angeles entitled “Luxury Eco-Homes go Net Zero Water for the California Landscape”. The following post outlines the key points of my talk that illustrate how to achieve Net Zero landscape design.
Greywater and rainwater systems are a sustainable, cost effective ways to irrigate your landscape and are key to achieving net zero water usage. To achieve Net Zero, the landscape design must be done intelligently, with the supply anticipated so that the available water will inform the demand that is generated. Similar to an income which determines allowed expenses, the landscape design may need to be adjusted in order to respond to the available water by adjusting the specified irrigation system and plant choices.
The equation to determine net zero landscape water use is: (RW+GW) – (Lwr+M) = 0
Where the supply [rainwater (RW) plus greywater (GW)], minus the demand [landscape water requirement (Lwr) plus irrigation modifications (M)] equals Zero. For example, a 5-person household produces approximately 50,000 gallons of greywater. This alone may be sufficient to irrigate a residential landscape. If rainwater is being harvested, then supply will vary based on the area of roof surfaces used for capturing the rainwater and annual precipitation in the specific location.
Lawns consume the greatest amount of irrigation water, with spray irrigation being the typical method for watering. It is against code to use graywater through these kinds of pop-up sprayers. The danger is that pathogens (from washing machines, for example) become atomized and airborne in this kind of system, enabling them to be inhaled and cause potential health issues. Therefore, subsurface irrigation has become the method of choice for greywater applications. Several types of subsurface irrigation can be employed. The most common utilizes drip emitters and capillary action where greywater is directed underground into a sand bed contained by a pond liner. The roots of the lawn above act like a natural moisture sensor, seeking the water, which water wicks up to the roots with capillary action.
This has to be calibrated carefully; if there is insufficient greywater (for example, if the homeowner is away on vacation), there needs to be a back-up source of water for the landscape. Rainwater or municipal water can provide this fail-safe and be connected to the irrigation system with an automatic valve.
Flow meters and flow monitoring are important components in any greywater or rainwater system as well. These tools allow the homeowner to track how much water is harvested and being used, and to identify any leaks or excessive amount of water being used. The homeowner can be alerted via email, allowing them to immediately address the problem.
With a thoughtful approach to landscape design, allowing the supply to inform the creation of demand, a Net Zero Water landscape can be achieved.