The Call and Times, Column 22 – Water, Water, Everywhere: Urban Rainwater Harvesting

7 08 2015

(June 7th, 2015)

The Urban Farmer

Water, Water, Everywhere: Urban Rainwater Harvesting

Remember that three-day stretch of nearly constant rainfall early last week? I have to admit, for every raindrop that hit my roof, I died a little inside. You see, there’s this one special project (well, there are hundreds, but I’m going to focus right now) that I’ve been meaning to do for years but have never gotten around to, which has become one of my latest obsessions: rainwater harvesting.

Otherwise known as rainwater catchment, this is exactly what it sounds like. By installing a waterproof container at the bottom of a downspout gutter, the rainwater that falls on that portion of your roof can be collected and stored for future use.

Later on, I will describe a simple catchment system (the basic plan that I will be using). But before we get into the practical, let’s talk theory: why exactly would I want to go to the trouble of installing rainwater catchment on my house?

Being a coastal state in the Northern Atlantic, Rhode Island is blessed with relatively rainy summers (though someone might want to remind the climate about that this year). With that said, rainfall often comes in short bursts of thunderstorms, while our farms, gardens, livestock, and people would probably be better off with a little water every day rather than a biblical flood twice a month. The basic motivation for rainwater collection is the same as many other homesteading projects – if you save it during times of plenty, you’ll have it during times of little.

For every inch of rainfall, a 100 square foot area of roof (the size of a small bedroom) passes 62 gallons of rainwater – more than you can shake an umbrella at. Taking the average roof area in our region to be about 1000 square feet (U.S. Census Bureau), and Rhode Island rainfall to be 3 to 4 inches per month, a total of nearly 20,000 gallons of rainwater falls onto the average roof in the 9 non-winter months every year! Because of how easy it is to harvest, those 20,000 gallons ($100, at our rates) of clean, free rainwater are essentially wasted in most homes in the country, my own included.

The rule of thumb is that vegetable gardens require 1-2 inches of water per week in the summer, including rainfall. It’s entirely possible that we could get this much rain, but there’s a catch: a garden does much better with frequent watering, rather than what would otherwise be a cycle of flood-drought conditions. By collecting and storing rainwater when it is abundant, it can be used to irrigation the vegetable garden during periods of little or no rain.

Being a frugal, environmentally-conscious, thinking-in-cycles, conservationist engineer, these numbers are too appealing to pass up. I will be constructing a simple rainwater catchment system in the next few weeks, and I’m writing this column to hopefully motivate you to do the same.

With that, the central question is: what do I need to build a minimalist rainwater catchment system? While I can’t give a complete tutorial here, I will address the different components (there really aren’t that many) of a rainwater collection system. The internet is full of step-by-step instructions about how to build these fixtures for very little money, and I would recommend http://www.instructables.com/ as a good place to start.

The first step in rainwater collection is the downspout. Most homes already have these, but they often have to be adapted (and probably shortened) so the water can run into your collection container rather than onto the ground. In addition, I’ve encountered many urban farms in my research that employ what is called a “first flush system”. This is essentially a clever piping system that discards the first few gallons of each rainfall. This is desirable, because asphalt roofing tiles that were hot prior to the rain can leach small amounts of heavy metals and volatile organic compounds (VOCs) into the first bit of rainfall. By stopping the first few gallons from going into the rain barrel, you prevent those chemicals from ending up in your garden. What’s more, it helps to remove most bird droppings.

The next step is the storage tank, commonly called a cistern or a rain barrel. This can be as big or as small as you like. Pre-assembled rain barrels or assemble-it-yourself kits of 50-100 gallons are available for sale online and from many garden stores for around $100. In my opinion, it is easier and less expensive to build one yourself.

A simple, sturdy trash can works just as well, and makes the whole enterprise much more cost effective. It must have a tight-fitting lid, to prevent animals and insects (mosquitoes) from getting in. To this, you basically have to add a screened hole in the lid for the water to enter, and a watertight spigot near the bottom, to which you can attach a hose, for water to exit. An overflow system is also a nice addition: essentially you make another hole on the side of the barrel, near the top, so that excess rainwater can feed elsewhere (another rain barrel, perhaps?) once the primary container is full. Again, I direct you to one of many DIY websites for specific instructions to suit your individual budget and needs.

Finally, there is the (optional) distribution system. The water can simply be taken as-is from the spigot – a watering can or bucket is all you need to disburse it to those organisms in need of it most. A hose can also be attached, allowing you to water manually.

In my opinion, the state-of-the-art distribution system is drip irrigation. By laying out special (or homemade) irrigation piping throughout your garden, you can deliver water directly to the roots of your plants, minimizing waste and reducing weed growth. This is my preferred system, and I will be building one sometime in the near future.

One other thing to consider: the higher the rain barrel is raised up, the more water pressure (and higher flow rate) you will have in the distribution system. This doesn’t matter as much if you’re using automatic or unmanned drip irrigation, but if you’re watering by hand, a higher flow rate means less time spent watering. Something as simple as inexpensive, cement cinder blocks can do the job of adding a few feet to the height of the container.

Rhode Island house bill RI HB 7070 of 2012 set up a 10% tax credit for the cost of installation of residential and commercial rainwater catchment systems. Rather than illegalize rainwater collection, as has been done in certain other states, Rhode Island is actually encouraging its residents to collect rainwater. And they do so for good reason.

It is healthier for your plants, healthier for your animals, and healthier for the environment. And while I would not recommend drinking it yourself (insect larvae, toxic compounds, algae and other microorganisms will undoubtedly be present in the water), collected rainwater serves as an important buffer against short rain-free periods, more serious droughts, and problems with the municipal water supply. Remember, my friends: resilience is the product of practical forethought.

My column appears every other Sunday in The Woonsocket Call and The Pawtucket Times. The above article is the property of The Woonsocket Call and The Pawtucket Times, and is reprinted here with permission from these publications. These are excellent newspapers, covering important local news topics with voices out of our own communities, and skillfully addressing statewide and national news. Click these links to subscribe to The Woonsocket Call or to The Pawtucket Times. To subscribe to the online editions, click here for The Call and here for The Times. They can also be found on Twitter, @WoonsocketCall and @Pawtuckettimes.

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