For some people, the idea of “free water” is no big deal. You might have a well or cistern on your property and don’t get a water bill. If you have a cistern, you essentially have one big “rain barrel” and this article may not be of much interest to you. If you have a well, it’s either a pump well or has an electric motor. If it has an electrc motor than you probably know well the challenges you face if the power goes out and you don’t have a back-up source of power. That prediction got me thinking about how we measure rainfal in inches and how much water it actually is. I had to do a little bit of research and some math but it wasn’t difficult. Any fifth grader could do it (I think). Here are the numbers. Bear with me as I justify the relatively low cost and simple expediency of having a rain barrel or three.

If it rains one inch, that means if you were using something with straight sides to catch and measure the rain, you would end up with one inch of water in your container. If your container is one inch square and fills one inch deep then you have one cubic inch of water. If your container is one foot square (twelve inches on both sides) then you have 144 square inches of water, one inch deep, or 144 cubic inches of water. There are 231 cubic inches of liquid in a gallon, so 144 cubic inches of water equals (approximately) 2/3 of a gallon. I applied this math to the square footage of my roof to figure out how many gallons of water would run off through each downspout.

Rain barrels are not difficult to set up and can provide a good amount of “free” water for your survival use.

My house is approximately 2,000 square feet and I used the same number for my roof. I know it’s actually greater due to the slant, but I really didn’t want to get into the necessary geometrical calculations to figure out the exact square footage: 2,000 square feet was close enough to satisfy my curiosity. Further my house has four downspouts servicing different sections of the roof. To know which downspout would be of greatest water collection value, I had to approximate how much roof was served by each one. (yeah, I know; this is boring. Bear with me another couple lines and you’ll see the value.) What I figured out was that my downspouts served as follows:

Downspout 1: 1/3
Downspout 2: 1/4
Downspout 3: 1/6
Downspout 4: 1/3

Downspout 1 and 4 service about the same amount of roof space, but Downspout 1 is located in my backyard while Downspout 4 is in the front of my house. For the sake of “hiding” my rain barrel and not potentially uglying up the front of my house, I chose Downspout 1. Remembering that my roof is about 2,000 square feet, Downspout 1 (servicing 1/3) services about 667 square feet. At 144 square inches per square foot that’s 96,048 square inches. One inch of rain equals 96,048 CUBIC inches of water. That’s just under 416 gallons of rain water – and that’s just from one-third of my roof space. According to my water company the average person uses 70 gallons of water PER DAY, so 416 gallons is six days’ worth of water for one person. Bear in mind that is NOT “survival” usage. To SURVIVE a person needs one gallon of water per day (according to experts) so 416 gallons is over a year’s worth of water for one person, or over three months’ worth for a family of four.

Another example of rain barrel set up.

Since the average rain barrel holds about 60 gallons of water, that one rainfall would have been sufficient to fill a rain barrel seven times (about). When I thought about all that water simply running off into my yard, as nice as my grass may look now, my thought was, “Holy crap! I’m letting a lot of free water just flow away.” Then I gave some thought to my water preparations prior to weather disasters wherein I was worried about losing my water supply. My family has six 5-gallon water jugs that we fill (30 gallons total), we fill both bath tubs (another 80 gallons total) and I count my hot water heater as well as all three toilet tanks (another 59 gallons altogether). That gives us a supply of 169 gallons of water. One 55-60 gallon rain barrel is 1/3 of that, but one 1″ rain fall on just 1/3 of my roof provides nearly TRIPLE that. Given all that math and thought, here’s reality:

It is simply foolish to let all that rain water flow away, especially since it’s SO easy to capture and store it.

Once I had decided to set up a rain barrel my question became, “Why set up just one?” Thanks to the power of the Internet you can do a search for “rain barrel” and find directions on how to set up daisy-chained systems that link more than one rain barrel together. The flow comes down your downspout, through whatever filtration you set up (discussed momentarily) and fills your primary barrel. When that barrel fills then it begins filling the next barrel. When the second barrel fills then it begins filling the next barrel. The last barrel in your chain has to have an overflow drain to allow excess water to run off. There are a couple good points about having such run off. First, it indicates that you’ve captured your maximum capacity of water. Second, you can direct the overflow drainage as you see fit, saving your yard from naturally occurring puddles, etc.

Now, let’s talk about filtration for a moment. Whether or not you intend to ever use this captured water for human consumption, you still want to filter it at least a little. Why? Because if you think about everything that comes off your roof such as leaves, gumballs, acorns, twigs, pollen clusters, etc. it’s easy to see how all of that would quickly build up at the bottom of your rain barrel. That would both make your captured water nasty AND eventually block your tap. If you buy a commercially produced rain barrel, shop wisely. Many of them come with filtration kits. If you choose to build your own rain barrel or buy one without a filtration kit, do yourself the favor of at least setting up a wire mesh filter to capture the big stuff you don’t want in your water/barrel. A section of window screen properly secured will work just fine.

One sample filtration system. The author describes another. This one obviously would not handle the volume generated by your downspout. The bottom line is that filtering is not hard but does require maintenance to the filter system.

If you want to filter your water farther than that, first understand that the water will likely never be “drinking” clean. After all, bird poop, squirrel waste, etc. all come off your roof, into your gutter and down that downspout. You can, however, filter it pretty thoroughly. If you’ve ever owned a fish tank and set up a multi-stage filter then you already know how to do this.

Start with a 3- or 5-gallon construction bucket. Cut a hole in the bottom 3″-5″ in diameter. Put a piece of that window screen over this hole INSIDE the bucket. On top of that put one to three inches of fine mesh type material: cotton balls, sponges, or purpose-manufactured filter mesh that you can get at your local pet store. On top of that put another section of wire mesh / screen. Next put in a layer of fine gravel two or three inches thick. On top of that put another section of wire mesh / screen. Next put in a layer of rough gravel two to three inches thick. Put a final section of wire mesh / screen on top of that. If you put a lid on the bucket, cut a hole 6″-8″ in diameter in the center of it and attach a section of wire mesh / screen ON TOP of the lid. The whole filter “system” goes on top of your rain barrel below the downspout from your gutter. You need to insure that the top of your rain barrel will support the weight of the filter system AND make sure the drain hole from the bottmo of the filter lines up with the input hole at the top of your rain barrel. Additionally, make sure there’s not a gap between the filter edges and the opening in the rain barrel where miscellaneous blowing debris can get in.

If you use this type of filter system you can be assured of relatively CLEAR water being collected. If you intend to cook with or otherwise consume that water you need to purify it first by either using water purification tablets or by boiling it. The filtration is not a “forever” system. The materials inside have to be removed, cleaned or replaced, and restacked inside at least once per month during rainy seasons. Off season (usually fall and winter) you can cut that back to every-other or every-third month (quarterly).

Some final notes: Build your rain barrel up on a platform at least two feet off the ground. That makes it far easier to get a watering can or other container under the tap. Additionally, make sure the rain barrel is sealed if it’s at all possible. Stagnant water is a favorite breeding ground of mosquitoes and you don’t want to help those potential disease carriers reproduce.

If you have ideas, comments or questions about rain barrels, please share them below!

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