We live in a desert. (Well, technically, we live in a steppe). It’s easy to forget that sometimes, especially when we live in a city lush with trees, lawns and golf courses. It’s even easier to forget in spring, the season filled with green possibilities, although this spring has been remarkably dry. Reality check time: Utahns are among the highest per capita water users in the U.S., and a large portion of this water goes to irrigate landscapes. As gardeners, we rely on irrigation to grow the majority of our vegetables and flowers in our high desert climate, and by using municipal water for irrigation we are jacking up our per person water tally dramatically. However, cutting our reliance on this water is simple, inexpensive and completely practical for anyone with a roof.
Would you believe it if I told you we get more than enough rainfall every year along the Wasatch Front to sustain a lush edible landscape without ever having to use a drop of chlorinated, fluoridated culinary water?
Since restrictions on its collection were loosened, more and more folks are collecting and storing rainwater. As simple as placing a barrel under a gutter’s downspout, we can capture our most precious dryland resource, store it, and irrigate with it later. It’s almost just too easy, and incredibly rewarding to boot. With an annual rainfall of 17 inches in the Salt Lake Valley, a modestly sized home can easily catch 10,000 gallons of water in the course of a year. That is plenty for the needs of a waterwise landscape and garden. Good, clean rainwater is the gold standard of moisture for our plants, free from chlorine, fluoride and other compounds found in municipal water. The key word there is clean, if we can catch it and bank it to utilize later.
Unfortunately, the air quality along the Wasatch Front ranges from poor to terrible depending on the season, and the last thing I want to do is concentrate these airborne pollutants into my rainwater tanks, then rinse them into my garden. Our roofs are also covered with bird poo, insect carcasses and other debris, which I don’t want festering in my rainwater tanks. The challenge, then, becomes how do we rinse the pollution from the air, clean our roofs, discard this water, and then collect the following clean water?
Fortunately, a Texan smarter than myself came up with an ingenious mechanism to divert this dirty first portion of a rain incident away from our storage tanks, a device known as the First Flush diverter. It’s commercially available. DIY instructions are also online.
The First Flush diverter is a simple assembly of plumbing that diverts a portion of the initial rainfall away from the collection vessel. Atmospheric pollution and other undesirable bits o’ funk are washed out of the air and off of our roofs with the first wave of rain, which then fills a specifically sized reservoir chamber. Once full, the following precipitation flows freely over the diverter chamber, and into your rainwater tank. (Note: I never collect rainwater during the winter inversion.)
Let’s take it from the top. Rain falls through the atmosphere, gathering dust and pollutants, then onto the roof catchment area, where it flows into the gutter system, then into the downspout. To keep leaves and large debris out, I use a screen at the point where the water leaves the downspout and enters the rest of the plumbing in my collection system. (A great unit called the Leaf Eater by Rain Harvesting is commercially available and priced right. See photo).
The water then moves through a 90-degree elbow so that it flows horizontally before arriving at our First Flush diverter. The top of the diverter is a “T” fitting, which uses gravity to send the first flow of rainwater falling down into our flush chamber. This dirty water fills the volume of the chamber and, once full, it becomes a simple aquatic bridge for the clean water to flow over. An upgrade on this system is a small plastic ball that floats up and seals the chamber, to keep any debris in the flush chamber water from being siphoned up.
The clean water then flows over the First Flush diverter chamber and into our cistern, and a valve at the bottom of the flush chamber allows us to drain the unit and ready it for the next rain. It’s a good idea to screen the entry point of your cistern, to keep out other debris, mosquitos and rodents. Don’t forget to plumb in an overflow on your cistern as well, because a hefty monsoon rain will fill most tanks remarkably fast!
To function properly, size does matter. If undersized, the water entering your cistern will still contain pollutants. If oversized, you’ll end up missing out on valuable collected water.
The first step is to calculate the volume of water to divert. Your roof and gutter system are the catchment area. When calculating the catchment area, we are only concerned with the footprint of the building, not the square footage of the roof, as the pitched roof area does not increase the total catchment area, ya dig? One inch of rain equals .6 gallons per square foot of catchment area, so a 1,000-square-foot home will catch 600 gallons of water with one inch of rain! In an area with minimal pollution, it is recommended to divert 0.0125 gallons per sq/ft of catchment area, and in areas of substantial pollution (all of us on the Wasatch Front) 0.05 gallons per sq/ft is recommended. This would mean a First Flush Diverter volume of 7.5 to 30 gallons, respectively, depending on the level of pollution in your area.
Now, let’s take this whole game up to boss status, shall we? When dealing with a few 50-gallon rain barrels, there’s not much more to consider, as those get drained quite quickly in the weeks following a storm. However, with larger storage volumes we run into a problem, as these will often hold water for months before being used. The last system I designed and built had a bank of cisterns with a storage capacity of 1,800 gallons, designed to irrigate a large garden through several months of drought.
In nature, surface water is constantly being moved and aerated, which keeps it vibrant and healthy. In the still belly of a large cistern, we have the opposite: anaerobic conditions, which breed stagnant, foul-smelling water. Nothing spoils the joy of utilizing stored water faster than a rank odor, and a subsequent questioning of its safety. Water craves cycling and oxygenation, so hook it up! With a small air pump and air stones, you can efficiently and effectively keep your stored water oxygenated and vibrant for extended periods of time. The units used to oxygenate aquariums can serve the same purpose in our cistern. They are incredibly energy efficient, and there are solar-powered models available as well, just in case you feel like going boss-and-a-half.
One final note: Make sure to black out your tanks to prevent algae growth, which can also muck up your water party. Most tanks made for water storage are already opaque, but for those of you on the DIY team who are using repurposed IBC totes or 55 gallon plastic barrels, protecting them from light will prevent algae growth as well as extend the life of the cistern by preventing UV degradation of the plastic. Options include painting your tank, or wrapping with black plastic or geotextile fabric. I like to dress mine up a little by covering the wrapped tanks with reed fencing for a little tiki party vibe.
So there you have it, clean rainwater, pure and simple. By harnessing a valuable resource that literally falls from the sky, you can easily lower your municipal water usage, saving resources and money. Since it is free of chlorine, which is toxic to all forms of life, rainwater is the ideal water source for providing irrigation to your garden without negatively impacting the microorganisms in the soil, and is the best water to brew compost teas with.
Good job, crew, living smarter and lighter on the planet, while having fun and working less; that’s a boss move.
Until next time, get outside, sleep outside, spend less time at work, and keep growing this thing.
James Loomis is a professional grower and consultant, and teaches monthly workshops on a variety of topics related to regenerative agriculture and urban homesteading. Facebook.com/beyondorganic
First Flush Diverter kit, complete with ball and release valve, is available from Rain Harvesting. $30-$40.