The opportunity for alternative water

Irrigation professionals can tap into gallons of on-site greywater and rainwater to help satisfy a landscape’s irrigation needs.

Stringing multiple rainwater tanks together can help maximize on-site storage while making it easier to comply with local building codes.
Photo courtesy of Dakotah Bertsch Landscape Architecture

Alternative water sources such as rainwater and certain types of wastewater can play a pivotal role in plant preservation and water conservation. The key is understanding where the opportunities lie in various landscape settings.

Recycled wastewater is a logical place to start because the typical household generates a lot of it, even during times of drought. Toilets and kitchen sinks must be excluded, but greywater from washing machines, bathtubs and bathroom sinks is perfectly appropriate for the landscape. While an irrigation system could not be set up to spray greywater due to the risk of contamination, more targeted delivery to specific trees and plant areas is feasible.

“Plants that have a higher value in the homeowner’s mind are the plants you want to irrigate with greywater, because greywater is something you’re always going to have,” says Sherry Bryan, water division program manager for Ecology Action, a non-profit environmental consultancy based in Santa Cruz, Calif. Those plants could range from fruit trees and vegetables to trees and shrubs with sentimental value. “You just don’t want the greywater to ever come in contact with the edible part of a plant,” Bryan points out.

You also don’t want to store greywater for more than 24 hours. “It will turn black because the skin cells and hair in it start to break down, breeding bacteria and developing a foul odor,” Bryan explains.

Installing a greywater surge tank outside of the house is an option when the cramped space beneath the home makes it impractical.
Photo courtesy of Dakotah Bertsch Landscape Architecture

An easy way to start going grey

A lower-cost, less complex way to implement greywater into a landscape is through a home’s washing machine. Laundry-to-landscape irrigation is easier to execute because there isn’t a lot of intricate plumbing that needs to be altered. You can also take advantage of the washing machine’s pump to get the water flowing to the landscape.

The washing machine’s drainage hose is connected to a three-way diverter valve which allows the homeowner to direct the water to either the landscape or the sewer. From that three-way valve, 1-inch PVC is installed to carry the water through the wall to the outside of the house. On the outside of the house, 1-inch HDPE tubing is connected to the PVC to carry water to the location of the plants. Tee fittings are then installed as needed to supply water to the individual plants at the roots.

“Water basins are dug around the plants and lined with mulch,” Bryan explains. That mulch helps filter the water before it permeates the soil. The basin fills back up every time the homeowner does a load of laundry.

“Mulch is the critical piece to a system like this,” Bryan says. “The mulch breeds fungi and actinomycetes that break down carbon bonds in hair, skin cells and other things found in greywater. So, you want to use wood chip mulch because it will grow the biology you need to break down that gunk. If you don’t have mulch, you will develop a disgusting biofilm on the soil surface that will not break down.”

Replacing the mulch on an annual basis is the one key maintenance component to a system like this. “You do not want filtration in these systems because they will clog,” Bryan adds. With a laundry-to-landscape system, the greywater is placed into the landscape right away, and the mulch provides all the filtration you need.

A greywater system’s surge tank can be stored under the house in a basement or crawlspace, so long as the tank is easily accessible for maintenance.
Photo courtesy of Dakotah Bertsch Landscape Architecture
PHOTO © NinaMalyna | Adobe Stock

More robust greywater systems

Greywater systems can also be more complex and versatile, so long as the property owner has the desire and budget.

“On a high-end residential or commercial property, a gravity-fed, laundry-to-landscape system limits the amount of plants that can be watered,” says Dakotah Bertsch, founder and principal of Dakotah Bertsch Landscape Architecture in Santa Cruz, Calif. “A pump-driven system allows you to put greywater from several household fixtures into a standard drip irrigation system that can go anywhere in the landscape.”

Bertsch typically collects greywater from bathtubs, showers and bathroom sinks, as well as washing machines. A plumber must go under the house and separate those drainpipes, running them separately from the sewer to a three-way diverter valve. That valve connects to a surge tank which then connects to the greywater irrigation system mainline. Bertsch tends to use surge tanks in the 200-gallon range, which allows the greywater to cycle through within 24 hours.

If practical, the three-way diverter valve and surge tank can be placed under the home in a basement or crawlspace — as long as they are easily accessible. Another option is to place them outside and, in the ground, next to the foundation. In either case, a plumbing stub-out is needed to get the greywater from inside the home to the outside landscape.

Easy access to the three-way valve is important so homeowners can divert water to the sewer during periods when their landscape irrigation system doesn’t need to run. For an added layer of safety, any greywater overflow in the surge tank is designed to spill over to the sewer by gravity. A one-way check valve ensures that sewage can’t get into the greywater system.

Easy access to the surge tank is also important. “I like to use a sock filter to help catch lint and hair when greywater is entering the tank,” Bertsch says. “The filter is removable and must get checked and cleaned at least every three months.”

The surge tank contains a sump pump to pump the greywater through post-filtration to the greywater irrigation mainline. “From here I like to use inline drip irrigation tubing to distribute water to the plants in the landscape,” Bertsch says.

A standard irrigation controller could be connected to the pump in the surge tank. For backup water, a float switch in the tank can add municipal water directly via an air gap. “You could even establish a direct cross connection,” Bertsch says. “When the surge tank is empty, the float switch operates an electronic valve that switches over from greywater to backup municipal water.”

PHOTO © Hamik | Adobe Stock

Rainwater catchment and irrigation

The other logical alternative on-site water source is rainwater. According to Bryan, the challenge for many homeowners is the required investment. In places like California, a lot of rain falls in the wintertime. It must be stored until the dry summer months when it is needed. Unlike greywater, rainwater is clean and can be stored. “Setting up a rainwater system is more expensive because you need large storage tanks,” Bryan points out.

Bertsch has designed high-end landscapes with tens of thousands of gallons of rainwater storage. He has developed a formula to estimate how much rainwater can be caught off the roof(s) on the property, as well as how much water the landscape needs.

“I’m usually spec’ing in 10,000 to 15,000 gallons of storage, but have gone as high as 100,000,” Bertsch says. “Some of those tanks get pretty big, often 30- to 50-feet in diameter and 7-feet high using metal siding as the structure with an internal liner.”

To make things simpler from a code compliance standpoint, Bertsch likes to use smaller 5,000-gallon polypropylene tanks strung together to achieve the desired storage volume. “On the other hand, some clients don’t want to look at rainwater storage tanks,” Bertsch adds. “When that’s the case, we design a large underground fiberglass tank.”

Much like with a smaller greywater surge tank, a rainwater tank requires a prefilter, pump and post-filtration element. The same maintenance considerations apply.

When designing landscapes with both a greywater and rainwater irrigation, Bertsch says it’s important to keep the two systems separate. For instance, greywater can be used in a drip irrigation system to water trees, flowerbeds and other plants. Clean rainwater could be used in a traditional sprinkler system to irrigate turfgrass or groundcovers.

For more complex greywater irrigation systems and rainwater catchment systems, cost can be a barrier for many. Bertsch tells his clients that they likely won’t see an economic ROI in their lifetime. Those who make the investment are quite environmentally conscious, and perhaps like the idea of having more on-site water in the event of a wildfire.

“My clients are also becoming more aware of the fact that the climate is increasingly unpredictable,” Bertsch adds. “The drought cycle is likely to continue. At the same time, population continues to grow. As water becomes more scarce, more people start to like the concept of water independence.”

July 2022
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