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Let’s get smarter about water by harvesting the rain

“Whether moved by rivers, held in lakes and aquifers, or suspended in giant ice sheets, freshwater is a precious resource to revere and respect, not least of all because we — and the plants in our gardens — rely on it for survival.”

— Matt Rees-Warren, “The Ecological Gardener,” 2021

I think we’ve all become more conscious of how precious freshwater is to life on Earth, but are we aware of just how much freshwater we use? See whether you can answer the following questions:

1. What percentage of the Earth’s freshwater is available for human use?

2. How many gallons of freshwater does an average American household of four use in one month? Over one year?

3. How many gallons of freshwater does your household use in one month? Over one year?

4. During June through September, how many gallons of freshwater do you use to irrigate your lawn and garden (at a conservative estimate of 30% of total household use)?

The amount of freshwater we use is shocking, particularly given the relatively tiny amount of freshwater that is available (see answers to the above questions at the end of the column). As with other precious natural resources, people tend to take freshwater for granted until we don’t have it anymore.

We need to act smarter about using water in our garden, and one way we can do so is by capturing rainwater and using it for irrigation. As UK author Matt Rees-Warren points out, harvesting and reusing rainwater provides a reserve of water that will help our gardens stay healthy during the dry summer months without overtaxing municipal water supplies (which, in Medford, come from Big Butte Springs and the Rogue River).

You might be surprised at the amount of rainwater that can be captured in the gutters attached to the roof of your house or other buildings. According to the OSU Extension guide “Harvesting Rainwater for Use in the Garden,” for every inch of rainfall, about 0.62 gallons of water can be potentially harvested for each square foot of roof surface. About 75% of that amount can be efficiently captured for irrigation.

For example, the roof of my barn is 800 square feet, so for every inch of rain that falls, I could capture 372 gallons of water (800 x .62 x .75). If it rains 20 inches a year (historically, about average in Medford), then I have the potential to harvest about 7,440 gallons of water from my barn roof.

Of course, most of us don’t have the ability to store that much water on our property, even over the course of a year, so how much rainwater would we need to irrigate our garden from June through September? Here’s an example:

Next to my barn, I have eight 8-by-4-foot raised beds that total 256 square feet. If I use driplines to supply an average of 1.5 inches of rainwater per week over half of that area, I would need about 2,000 gallons of water over the four-month period. A 2,000-gallon vertical water tank has a diameter of 7.5 feet and a height of about 7 feet, which means I could easily store the tank behind my barn.

A water tank of that size costs about $1,500 (or 75 cents per gallon of rainwater stored). An alternative to storing rainwater is to divert the water to a pond, swale or rain garden on your property. This slows down run-off so more rainwater can be used for irrigation.

I hope I’ve piqued your interest about rainwater harvesting. Even if you can’t harvest rainwater at your home, you can become actively involved in a rainwater catchment project at the Southern Oregon Research and Extension Center.

Last September, the irrigation wells at the SOREC campus on Hanley Road ran dry, so watering all the demonstration gardens and the native plant nursery stopped. A temporary watering system was put in place, but the Master Gardener, Small Farms, Land Steward and other programs housed at SOREC are now raising money to install a large rainwater catchment system. The 5,000-gallon system will capture rainwater from the roof of one of the greenhouses.

The harvested rainwater will be used to maintain native plants in the nursery on campus. The system will also serve as a teaching tool so community members can learn how a large capacity rainwater catchment system operates. Interpretive signs and brochures will be placed with the system for the public’s information.

To learn more about the rainwater catchment system or to make a donation, visit the JCMGA website at https://jacksoncountymga.org.

In the meantime, here are the answers to the questions I posed at the beginning of the column:

1. Just 3% of the Earth’s water is freshwater; of that, only about 0.5% is available for human use.

2. An average American household of four uses about 12,000 gallons of water per month or 144,000 gallons per year.

3. If you use municipal water, check your water bill to see water use calculated in thousands of gallons per month; add up monthly usage and divide by 12.

4. If you use municipal water, add June through September thousands of gallons used and multiply by 0.3.

Rhonda Nowak is a Rogue Valley gardener, teacher and writer. Email her at Rnowak39@gmail.com. She hosts a monthly podcast “Celebrating Women’s Work with Plants in the Rogue Valley” at https://mailtribune.com/podcasts/the-literary-gardener.