Going Grey: Reusing Wastewater for Your Desert Oasis

  • Jenn 

I have a memory of boating on Lake Powell with my family. The lake was full. Blue water lapped across the red rocks, and its depths were magnificent. When you jumped in, you could see your feet clearly treading water, suspended hundreds of feet above the of darkness of the flooded canyon floor. 

Drought in the West

Almost my entire adult life, the West has been in a drought. When I see the white calcium rings that now climb out of Lake Powell’s waters, that memory seems unreal and dreamlike. Every foot the water sinks from the top of that white line heightens concerns about what is yet to come.

While Lake Powell is low, the real concern for Arizonans is farther down the line at Lake Mead. Lake Mead is now expected to hit 1,050 feet of elevation by the summer of 2020. That is the point at which a Tier 2 water shortage will be declared, and food producers in Arizona will start to lose some of the water they have always relied on to grow their crops.

Reclaiming Water for Your Landscape

In the face of Arizona’s water shortage, it makes more sense than ever to reclaim water from your home to irrigate your landscape. While many states still prohibit greywater use, Arizona, New Mexico, and Texas are leading the way in reclaiming water for residential properties. In fact, Tucson passed the Residential Gray Water Ordinance in 2008, requiring greywater stub outs to be included in new home construction projects.

Our home is not new. Built in 1954, our mid-century ranch is a DIY labor of love inside and out. We installed a laundry-to-landscape greywater system in April of 2017. With this system, we divert the majority of the water from our washing machine out into our yard to water the large established trees on the west side of our property. We have also added new plantings of shrubs and native deer grass that are watered by the washing machine as well.

What you Need to Know before Installing a Greywater System

We worked with Watershed Management Group in Tucson to install our system. In the laundry room, Mr. Modernita installed a diverter switch and pipes to carry the water from the washing machine out into the yard. Watershed Management Group finished the system, running irrigation line to the trees and creating a basin to hold excess water. It is a simple branched system, like this one developed by Oasis Design.

Your Laundry Detergent Can Kill Your Plants

Moving to a greywater system has required some changes in our laundry habits though. Figuring out how to optimize the system to support healthy soil and landscape plants has taken a good amount of research. I’ve learned that even eco-friendly soaps meant for greywater systems can contain ingredients that are harmful to plants when they build up in the soil over time. For example, many laundry soaps contain salt, and most plants are not adapted for salty soil. Those that do not contain salt often contain baking soda. The problem is, baking soda is alkaline and can make the soil more alkaline as it builds up over time. In Tucson where our soil is already highly alkaline, this can interfere with a plants ability to thrive.

I’ve landed on Oasis laundry detergent as the best option for our family and our plants. It is hard to find, which is annoying, but it’s currently available on Amazon. (This is not an endorsed post. Neither Amazon nor Oasis have any idea who I am.)

Oasis Detergent Actually Helps the Soil

The reason I was excited to learn about Oasis is because it breaks down into carbon dioxide, water, potassium and sulfur. Sulfur is useful in making soil more acidic, so it is often used as a soil conditioner in desert gardens to make non-native plants perform better. I recently tested the pH of the soil in an area that receives a lot of water from the laundry-to-landscape system and found that the soil there registered a bit lower on the pH scale than soil elsewhere in the yard. It was slightly closer to neutral. This is an exciting find for a gardening geek like me!

Ordering a gallon of Oasis laundry soap from Amazon is considerably more expensive than buying Ecos in bulk at Costco, but I tell myself that I’m saving money on the soil conditioners that I might otherwise be buying.

The other change that I’ve had to make since switching to a greywater system is spreading laundry day out over several days during the week rather than doing it all in a day. When the weather is hot and dry (hello May and June) you have to water frequently. By doing the laundry every other day or so, the plants have a steady supply of greywater to quench their thirst.

Considering the predictions that drought will become more and more of a problem as the Earth warms, it only makes sense to reuse water from your home to irrigate your landscape. In the meantime, you will also enjoy lower water bills as you recycle all that gently used greywater to water your landscape plants.

Editorial note:

There seem to be many different spellings for greywater/gray water on the internet. I’ve chosen to stick with “greywater” for consistency except in the name of the Tucson City Council Ordinance, where I have used the official spelling from the ordinance title.

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