Greywater Irrigation: Laundry to Landscape

Laundry to Landscape is a washing machine pressurized irrigation method, explicitly mentioned in the California greywater code.

The basic concept is connecting a 1″ or larger hose connected to the outlet of the washing machine, and running this hose as long as required to reach the irrigation area. Either holes are drilled into the hose, or adjustable valves are then added to allow the graywater to empty into mulch basins around trees and plants.

Advantages:

Material Cost:

This method is relatively low in cost, typically $200+ for materials, + labor.
The irrigation layout is less demanding of grade (fall) than the branched drain network.

Laundry to Landscape

Laundry to Landscape schematic

This diagram is not an endorsement of the method, and should not be used as a construction guide. Use of this method will void the washing machine warranty.

Disadvantages:

Reliance on Mulch basins:

Because of the relatively limited number of outlets, mulch basins are required to catch the sudden flow of water. As with branched drain networks (although not to the same extent as it is easier to create more basins with Laundry to Landscape), this method is really only suited to trees, and the trees will still require extra feeding due to the limited root growth that will occur.

In most cases the ideal number of mulch basins is 10, balancing load on the washing machine vs. even water allocation.

At best, the graywater re-use will only be 30% efficient.

Uneven flow rate across irrigation points:

The water pressure inside the pipe at each irrigation point will vary according to the flow rate at each point, the distance of the point from the washing machine, and how much water the washing machine is pumping out at any one time.

Much time and effort is required to tune numerous valves to achieve consistent, even irrigation.

Lack of filtration causes clogging.

Washing machines can produce a significant amount of lint and hair. This rapidly clogs any pressurized irrigation system unless additional filtration is used. A simple but reckless solution is to place a filter sock (or similar) on the washing machine outlet. However this places even more load on the wash pump.

An alternative method is to use large holes in the irrigation tube. The large holes won’t clog as easily, however tuning such systems to water more than one area takes trial and error to achieve even watering. A garden hose service connection can be used to flush the line at pressure, however may not clean a single blockage if the other holes are clear.

Washing machine pumps are NOT built for this.

Plumbers and appliance stores have made a LOT of money in Australia either repairing or replacing washing machines.
About 5 years ago major hardware chains started selling 1″ hose kits. The kit couldn’t be simpler, a 1″ hose, with a rubber connection on one end and simply open at the other. People simply connected the hose to the outlet, and moved the hose around the garden from wash to wash.

Even with a totally open hose (in most cases 30′ long), many washing machines failed within 3 years use. Pressurizing the washing machine pump by restricting the flow via valves etc places even more load on the pump.

Irrigation inefficiency

To minimize damaging backpressure on the pump, a series of holes/valves are used, ranging from 1/4” to 1” in diameter. To avoid clogging of the holes, at least a 3/8” hole is recommended. According to the Oasis Design‟s calculator about 10 holes are required to avoid overloading the pump / achieving uneven distribution.

A mulch basin for a tree is typically about 4‟ in diameter or 12.6 square feet. The total irrigated area with 10 mulch basins will be 126 square feet.

However, assuming an ETo Value of 7” per month (peak summer average across the more heavily populated regions of California), the optimum irrigation area is:

Low water use plants         1,451 square feet     (c/w L2L efficiency 8%)
Medium water use plants     839 square feet     (c/w L2L efficiency 15%)

It is possible if washing is done on a daily or every second day, that capillary irrigation effects will assist, however at best this is likely to double the efficiency of L2L up to 30%.

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