That may sound like a frightening statement, but surprisingly, it’s not necessarily true. There is water available to our gardens; maybe we just haven’t noticed it. As I write this column, it’s Thursday morning. Forecasters are predicting between one half and one inch of rain in the next 48 hours. That’s a lot of water; precious water. Water that your garden may need later.
Some of that rainwater is falling onto your garden and watering your plants, hooray. But a lot of it is lost.
Urban roofs and how they deal with rainwater are a fascinating study. Consider that your rooftop has been carefully designed at a gentle slope, for the sole purpose of shedding any water that might fall on it. Along the edge of that well crafted, sloped roof is another engineering marvel, a rain gutter. Your roof and raingutter are perfectly coordinated to collect every drop of precious rainwater. The collection and diversion of rooftop rainwater is a nearly perfect system. But what happens to all that rainwater, so masterfully collected?
At a couple of roof corners all that precious water is fed into a couple of collection tubes, called downspouts. So far, so good. In fact, it’s an amazing sight to watch, driving down a street while it is raining and seeing all that water, being perfectly collected, home after home.
But here’s the punchline. What do we do with all that collected rainwater? We move it swiftly and efficiently off our property and into a storm channel.Oops! Our gardens need it, not the storm channels.
Now look this picture. That’s a 620 gallon water storage tank. It’s sitting next to a raingutter downspout. Let’s assume that a typical home roof in the Newport Beach, Costa Mesa area is 1,500 square feet. That’s probably pretty close. How much rainfall would it take to fill a tank this size? The answer - about two thirds of an inch would fill the tank with pure, clean and free water; water to garden with.
The tank in this picture isn’t very big and fits flat against a wall, where it is hardly even noticed. It’s a closed tank with no mosquitoes or algae. Just pure, clean water. A hose bib provides the water to the gardener. Connections are even available to hook it up to an irrigation system. Of course, larger tanks can store even more water. In a year of average Orange County rainfall a roof this size will yield almost 12,000 gallons of free irrigation water.
In addition to supplying water, rainwater harvesting is also effective in reducing stormwater pollution. When rain falls, it’s clean, but it picks up pollutants along the way. This pollution is carried into storm drains and then to channels and ultimately into the ocean. Collecting stormwater from rooftops and directing it to storage tanks so it can later be used for irrigation decreases the volume of runoff and protects our coastal waters.
Before the creation of public water utilities, rainwater harvesting provided water for many American homes. It is still popular in places with limited water resources, such as the Middle East, India, Africa, the Caribbean, Australia and Israel.
In the United States, rainwater collection rebates are becoming increasingly popular, including cities like Albuquerque and Santa Fe NM, Austin TX, Denver CO and some communities around San Francisco. The city of Santa Monica offers rebates of up to $500 for diverting downspout water into these collection tanks. A couple of large garden centers, including Roger’s Gardens, are now demonstrating these rainwater tanks and even offering installation and set up options.
There is water available for your garden; perhaps you just haven’t noticed it.
Questions from Readers January 31.
Ron Vanderhoff is the Nursery Manager at Roger’s Gardens, Corona del Mar.