Graywater is untreated household wastewater that has not come in contact with toilet or kitchen sink waste (blackwater). Graywater comes from the washing machine, bathroom sink, shower, and bathtub, and makes up 50 – 80% of all wastewater of a residential home. Reusing this water is an excellent way to utilize resources that would otherwise be wasted. It can be used to irrigate small to medium sized areas of the landscape in close proximity and down slope from the source.
Trees, fruit trees, shrubs, perennials, non edible parts of vegetables and any salt tolerant plants may be watered using graywater. Graywater is ideal for sites with good soil percolation, buildings with raised foundations to allow pipes to be installed, and for families that utilize the washing machine, sinks, and showers often.
Graywater can also be used for toilet flushing. Either plumb a bathroom sink directly to toilet tank for immediate use or collect and treat Graywater in a central location and redistribute to all toilets in the house.
Graywater systems must use organic soaps that have lower salt content. Avoid products with sodium compounds, boron, chlorine, high pH, and other toxins found within body cleansing products.
Special Considerations Before Installing a Greywater System
- Access to drain pipes
- Slope of the land
- Drainage/ Infiltration of the Soil
- Proximity to creeks and waterways (minimum 100 ft. away)
- Quantity of graywater produced
- Irrigation needs of plants (suitability for graywater)
- Desired maintenance level
- Permit needs and budget
Types of Greywater Systems
- Laundry to Landscape – Washing machine pumps graywater directly to plants (no storage tanks).
- Laundry Drum – Washing machine pumps graywater to a barrel which then drains from the barrel through a hose and out to the landscape.
- Branched Drain – Gravity causes graywater to flow outside through pipes to mulch basins around plants. Must be on a slope with adequately sized outlets.
- Pumped System – Graywater drains to a surge tank where it is pumped out to landscape plants.
- Constructed Wetlands (Reed beds) – Graywater drains through a constructed wetland which removes nutrients and transpires water. Best when soil percolation is slow, space is limited and large volumes of water need to be treated.
- Sand Filter to Drip – pressurized system that removes particles with a sand filter, which allows the water to be clean enough for use in a drip irrigation system.
A Word About Greywater and Landscapes: Sodium, potassium, and calcium are alkaline chemicals that are present in laundry detergent. Because of this, graywater tends to raise the alkalinity of the soil. Slightly alkaline soils will support many garden plants. Even most acid loving plants will be happy with slightly alkaline soils that are generously amended with organic matter. The pH of an acid soil is 6.9 or lower while that of an alkaline soil is 7.1 or higher. If a simple pH test of the soil indicates a pH reading over 8.0, the pH should be reduced. This can be accomplished by adding agricultural sulfur or an acidifying fertilizer such as ammonium sulfate. Shade and acid loving plants do not like graywater. Their native habitats are forested areas where acid soils predominate.
Here is a list of plants that are not suitable for the alkaline conditions often associated with graywater irrigation:
- Azaleas, Begonias, Bleeding Hearts, Camellias, Crape Myrtle, Deodar Cedar, Ferns, Foxgloves, Holly, Hydrangeas, Gardenias, Impatiens, Oxalis (wood Sorrel), Philodendrons, Primroses, Redwoods, Rhododendrons, Star Jasmine, Violets
The following list of plants typically do well with graywater irrigation:
- Agapanthus, Arizona Cypress, Australian Tea Tree, Bermuda Grass, Bougainvillea, Bush Olive, Cottonwood, Honeysuckle, Ice Plant, Italian Stone Pine, Juniper, Oaks, Oleander, Palms, Purple Hopseed, Roses, Rosemary, and many native plants
Resources:
Washing Machine Greywater Sump, San Luis Obispo County Planning & Building, SLOPLANNING.org