Do you like paying your water bill? Do you know where the water comes from? How it is treated?
Rainwater harvesting is the use of rain for things like watering plants and trees in your yard (in “rain gardens“), instead of letting it run off. Sometimes the best things in life are free.
This is an ancient, inexpensive, and effective sustainability practice that is used around the world. It’s brilliance is in its simplicity. Nature and gravity do all the work.
Rainwater harvesting is well known in drylands such as the desert in Tucson, AZ where I live, but can be very helpful in many regions. Areas with heavy rainfall and flooding may benefit as well.
You may have heard of “xeriscape” and “drip irrigation”, but this takes things one step further. Rainwater harvesting, paired with native plants and trees, can be extremely efficient—and beautiful.
Podcast
Rainwater Harvesting in Action in My Yard
Video: One portion of our roof and our patio cover feed this basin via gutter/downspout/pipe. When this first basin fills during a rain storm, it can overflow into second, third, and fourth basins covering a large portion of our backyard. We also have several other portions of our roof that feed other areas in our side and front yards in much the same way.
Thinking Differently
To me, the concept of rainwater harvesting really makes sense.
I remember thinking this as a kid: “Why isn’t all food 100% organic, as it was for millennia?”
I now also think “Why isn’t rainwater harvesting the default design for many water systems, with supplemental water from modern systems that require dams, pumping water, which creates channelized storm runoff, and overdraws from ground water sources for short term gains?”
You may have also wondered why we use treated potable drinking water to flush our toilets, for example. Seems wasteful (pun?). In much of the developed world, high-quality potable water is used for all end uses. This wastes money and energy and has unnecessary environmental impacts. Using rainwater for non-potable water uses, such as toilet flushing and irrigation might be something to consider. Communities are working to redefine what water is appropriate for different uses and new (actually old) thinking about free rainwater is helping to update city water systems.
Tucson’s residential grey water guide document shows that about 45 percent is for yards/landscaping. That is a lot. By using rainwater harvesting you can really cut down on that number. Setting up a grey water system can also really help:
How Does it Work?
Rainwater can be captured from roofs or other surfaces and directed towards basins (“passive” harvesting) or stored in large water tanks for later/gradual use (“active” harvesting). The primary use for this rainwater is often to grow plants and trees in residential yards, but this concept is also being embraced by cities and in commercial/governmental/educational lots.
City governments and nonprofits are picking up on this trend. Tucson provides rebates to residents who implement projects. Local nonprofit WMG has classes and certifications available.
Tucson is implementing green storm water infrastructure projects (GSI) such as diverting water from streets to basins, creating native tree-lined, cooler streets. Green stormwater infrastructure (GSI) describes practices that use natural systems (or engineered systems that mimic or use natural processes) to capture, clean, and infiltrate stormwater; shade and cool surfaces and buildings; reduce flooding, create wildlife habitat; and provide other services that improve environmental quality and communities’ quality of life.
How Much Rain Falls On My Roof?
Answer – it is a lot!
Imagine you live somewhere with 10″ of rain and you have a 1,500 sq ft roof. When performing these calculations you can simply measure around the perimeter your home at ground level since it doesn’t matter what angle your roofline has.
Harvested rainwater maximum collection (gal) = (roof length x width (ft2)) x rainfall (ft) x 7.48 gal/ft3
So for our example: 1500 ft2 x (10in/12in) ft x 7.48 = 9,350 gallons per year!
Other Considerations
Common Misconceptions
- You don’t always have to purchase expensive tanks/cisterns. Actually, digging basins and having water from a roof fill them up is very inexpensive, or free, and is often step 1.
- You do want to use tanks/cisterns that are relatively large if possible. A 50 gallon drum will be filled rapidly when it rains, or even multiple strung together.
- Rainwater harvesting isn’t only for people living in the desert. There are many benefits for various regions.
- It often works really well. But you should probably have a plan for your yard, versus just starting out randomly. That being said, starting small and observing things can be very helpful.
Many Benefits
- It takes a lot of energy and resources to treat city water. Our water in Tucson is pumped from hundreds of miles away, up over mountains, and this is mostly done with coal power at the moment (major climate change implications). After the water arrives in town it must be treated and distributed. There is a lot of evaporation that occurs a long the way, from open aqueducts in blazing sun. That doesn’t feel like a sustainable design.
- You may be able to turn off or drastically reduce the use of your sprinklers and drip systems like I have, and primarily rely on rainwater for the plants and trees in your yard.
- Shade! My desert yard is much cooler than the all-rock, flat original design. The cooler each of us can make our own yards, the less AC is needed by surrounding homes, which lessens the urban heat island effect (the “exhaust” air from AC’s is very hot).
- Rainwater is often very pure and plants love it! Our city water is very hard and it seems to take a much larger volume of it to keep the plants at the same happiness level.
- If you live off a well or in a remote area rainwater can help with supply issues.
Passive Harvesting Examples
- During rainstorms water can be captured from roofs and diverted to basins in a yard. These basins can have grasses and shrubs in them, and shrubs and shade trees near the upper edge and beyond.
- Passive harvesting is pretty simple, inexpensive, and effective.
Active Harvesting Examples
- Using a large cistern (or multiple) to hold hundreds or several thousands of gallons of water to be used at a later time, such as during dry spells.
- Watering basins and trees as needed during those long dry periods when water from a roof isn’t reliably supplying enough volume to keep everything happy.
- Some people create outdoor showers that use water from a cistern.
- Using the water for veggie gardens.
- Although more complex, some filter the water and direct it indoors for uses such as washing clothes, for drinking water, etc.
In both passive and active scenarios, the water can sleep through the earth and replenish groundwater stores, versus being diverted to storm water drains and/or channelized structures.
Other Synergistic Techniques
- Grey water harvesting. Using water from your laundry is a common implementation. See my article about my home’s system.
- AC condensate harvesting: HVAC systems often drip condensate just outside of your home and this water can be captured and used in your yard. In summer months the amount of water can really add up.
My Experience
I had local nonprofit Watershed Management Group come out for a consultation and they create a plan for our yard(s), after taking one of their rainwater harvesting city rebate courses. A big bonus was that the city of Tucson provided a rebate for a part of the project. A major feature of our design is the pollinator garden section, which draws bees, birds and other pollinators. Our dog also loves walking around and smelling everything! Over a period of time I interpreted and implemented the plan, mostly by using a $10 shovel from Lowe’s.
Every time there’s a major rain event I carefully observe how the basins are doing and make adjustments. Upkeep is required, you need to add more mulch to basins and walking paths periodically, but the system mostly takes care of itself, due to its simplicity. Gravity does almost all of the work.
I also took a WMG course on grey water harvesting. Our clothes washing machine now directs water to two of our rainwater basins and the flow is adjustable. We use a special detergent that is grey water friendly (Ecos free and clear, or Oasis) and we grow some fruit trees in the primary basin that is fed. Read my grey water harvesting implementation article.
Site Photos
Don’t Live in Tucson?
Have a look at what your community may be doing about these issues, what rules/regulations might be in place, and share the model Tucson and others have implemented!
Helpful Links
- Brad Lancester from Tucson, AZ has an excellent website harvestingrainwater.com and book series. His work is thoughtful and comprehensive, it integrates permaculture themes, so please take a look! His Dunbar/Spring neighborhood is worth a visit (or Google Street View) as many of these techniques are on display on the streets, with educational guides along the shady paths. He also works with the larger community and watershed by training citizen foresters to plant and tend the rain and their food forests with his NeighborhoodForesters.org efforts.
- See Tucson nonprofit Watershed Management Group’s home consultation services such as creating a plan for your yard, and rainwater/greywater harvesting city rebate courses
- Tucson Water Harvesters Facebook Group Super helpful community! Do you have questions about rainwater harvesting and greywater projects?
- City of Tucson Residential Rebate programs such as rainwater/greywater harvesting, low flow toilets, water usage assessments, etc
- My grey water harvesting implementation article
- City of Tucson green stormwater infrastructure (GSI) aka Storm to Shade program
- Simple summaries on TreeHugger and Wikipedia.
- The Pacific Northwest National Laboratory (PNNL) in collaboration with the Federal Energy Management Program (FEMP) developed an online GIS-based Rainwater Harvesting Tool to help federal agencies strategically prioritize commercial rainwater harvesting projects by providing rainwater harvesting potential across the United States.
- Rainwater Harvesting Tool – Federal Energy Management Program. Also see their Rainwater Harvesting Systems Technology Review.
Questions?
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© October 11, 2024 Chris Graber