An average four person household sends approximately 38,000 gallons of water down the drain each year from their bathrooms and washing machines. We don't know what the future holds for our water supply. Therefore, graywater systems are important alternatives.
The elements of a system:
- Pipes that transport the greywater from inside to outside.
- Distribution plumbing: pipes that transport the greywater from just outside to the locations throughout landscape
- Surge tank and filter: optional - makes distribution easier, but is more expensive
- Receiving landscape: soil, roots; plants that contain, cover and purify the greywater.
A residential client of ours in the east bay has taken on an ambitious renovation of their large home and landscape. The owners' vision of their house is that it be a demonstration of sustainability for neighbors and friends. The project is expected to achieve LEED Platinum status. Some of their extra points are a result of three individual systems:
All the water from bathroom sinks, tubs and showers go through a filtration system, into a collection area, then is diverted into the landscape. Their plan is to generate 120 gallons of water per day.
Note: there are flush requirements, meaning that there is a limit to how much water the system can hold before it needs to be flushed into the landscape or the sewer system.
2. Laundry Water System
Separate from the graywater from bathroom sinks and showers, this water also is simply drained into the landscape. Plants are specially selected to tolerate a high level of phosphates (from the soap).
A consideration about this system: the soaps used in the washer. Experts recommend not using liquid fabric softener or harsh detergents and to use low sodium products. The most damaging chemicals for plants are boron, borax and bleach.
3. Rain Collection/Harvesting
The roof is composed of laminated solar panels. The plan is for rain to collect on the roof; pass through grates (which are a sort of filtration system) and then down to 15,000 gallon tanks. Water will be used in showers and sinks.
Note: a roof for a 1,000 square foot house can collect around 600 gallons per one inch of rain!
Graywater systems do require maintenance and in certain situations they are not the most sustainable approach. Here is a list of considerations:
- They may not be allowed in certain municipalities
- A permit is required unless it is SFPUC "laundry to landscape" program.
- If your soil is not permeable enough, the recycling of greywater may not be feasible or could be expensive to implement
- If your garden area is too small it may not be worth the investment.
- If the graywater system requires more maintenance than a properly functioning septic or sewer system it may be more sustainable to not pursue this option.