Reusing wash water for landscape irrigation can be a simple eco-friendly project. Many municipalities have regulations that govern residents' use of grey water, but if you reside outside city limits you may have the freedom to design your own system. One abundant source of grey water — that is, non-toilet water used for washing — is your washing machine, which processes an average of 41 gallons of water per load (see References 1). Divert that water into the outdoor environment instead of into the septic system for truly green living.
For non-regulated residential locations, bypassing the septic tank is as easy as removing the washing machine drain hose from the standpipe next to the machine, and then placing it in a pipe you have installed that drains the water to a barrel. Alternatively, you can drain the wash water directly to an irrigation network that you have installed throughout the landscaping. This might consist of a series of connected 1-inch PVC plumbing pipes in which you have drilled small drain holes. Retail drip irrigation systems may become clogged with small particles in the grey water, so they may not be a good choice. Alternatively, if you use a barrel for grey water collection, you can hand-water from there using smaller containers. Be aware, however, that you should not store untreated grey water longer than 24 hours in the barrel. (See References 2)
Often, cities and counties have health regulations for using residential grey water that are intended to protect the fresh water supply from contamination. For example, San Luis Obispo County in California requires that residents reusing laundry water install a sump, which consists of a gravel-filled trench, to filter out the contaminants in the grey water as it flows into the landscaping. Additionally, because water in which diapers or sickbed linens have been laundered can contain pathogens, the county requires that homeowners ensure such wash water is properly disposed of in the septic or sewer drain. (See References 3) Research your location's grey water regulations before starting to recycle.
Grey Water and Landscaping
To optimize the benefits of grey water irrigation, you should select laundry additives with care. While a modest amount of phosphorus in laundry soap may have a positive effect on plantings, soaps containing sodium for water softening can build up in the soil, causing it to become alkaline and unfavorable to the health of many plants. Therefore, using detergents that are low in sodium results in a greener landscape. (See References 3)
To keep grey water contained within your own environment, avoid irrigating sloped areas where runoff could encroach on property lines. When watering vegetable gardens keep the grey water at ground level rather than sprinkling from above, to avoid contact with the produce itself, except in the case of root vegetables. Alternating grey water irrigation with fresh water irrigation can help flush any grey water impurities deep into the soil, which acts as a natural filter to further clean the water as it absorbs into the earth. (See References 4)
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