You might be familiar with the concept of 'net zero' as it applies to energy use in green home design. A net-zero energy house produces enough energy than it requires to function, and in some cases, creates excess energy to feed back into the grid. Well, a similar concept can be applied to your home's water usage. Net zero water status basically means achieving independence from municipal water sources. In order to do this, the design must follow best practices in water management, providing provisions to:
- Capturing rainwater
- Managing stormwater runoff
- Reusing gray and blackwater
Rainwater is free for the taking. The term includes any water that strikes the surface of a building and is collected (once it hits the ground, it's considered 'stormwater'). By installing a rainwater harvesting system, which is available in either roof catchment or groundwater catchment formats, you can capture rainwater in order to treat it for use in your home or to irrigate your landscape. In a roof catchment system, the most common type, a series of gutters and downspouts conveys the water to a barrel or other storage device. This water can be reused to irrigate your landscape, or even used inside the home for laundry or flushing toilets. When treated with ultra-violet rays and other processes, rainwater and can sometimes be used for drinking, if allowed in your city.
Managing Stormwater Runoff
When not connected to a municipal sewer system, it is important to manage stormwater runoff on your property. Capturing excess rainwater is one way to help manage stormwater runoff. Other techniques include installing a green roof to absorb the excess or using pervious pavement to absorb rain that would otherwise rush along an asphalt or concrete surface. Certain types of plants also help to prevent the erosion of soil and dirt, and you can even go as far as to create 'constructed wetlands' in your yard that help to purify rainwater.
Re-using Gray and Blackwater
Graywater and blackwater are essentially wastewater. Graywater is water left over from running the sink, doing laundry or dishes, or taking a bath or shower. Blackwater, on the other hand, is water discharged from the toilet. Obviously, neither type of wastewater is suitable for drinking, but they can be treated and re-used for other purposes. Using a "Living Machine," which contains plants and bacteria and even some types of animals such as snails or clams, gray water can be filtered so it can be reused for household purposes. Composting toilets provide a way to manage blackwater, so you can turn it into compost for your garden.
At this point, there are few truly net-zero water buildings in existence. However, it is one of the rigorous requirements of the Living Building Challenge (LBC), a green building standard, so it could potentially become more common.
Net zero water is not easy to achieve. Is it practical or realistic for the average homeowner? Probably not. In fact, it might not even be illegal depending on where you live due to building code restrictions.
And for those who live in arid climates? Forget it. But you can certainly benefit from instituting some of these water conservation methods, no matter where you live.