Rainwater & Gardening

There is a gentleman in town who has a perpetual garage sale going. He has a space rented in town where he hosts a church in which he is a minister. In his off time, he goes and buys the contents of delinquent storage rentals and resells these goods in the same space as his church. As you can imagine, he winds up with some of the most random stuff conceivable. We make it a point to go by “Mikey’s Eternal Garage Sale” (our name, not his) every weekend or so. I have many stories to tell about things that I’ve purchased there, but this entry is about one thing in particular.

As I’m sure you are aware, we wound up with a fairly sizable home garden this year through a twist that is only possible in today’s internet-connected world. Jennifer has been writing about our adventures in gardening. Anyway, at Mikey’s Eternal Garage Sale (MEGS?) I saw a 55-gallon barrel made of blue plastic, probably high-density polyethylene. Mikey told me that he would sell me the drum for $5 if I wanted it, but wondered what in the world I wanted it for. I told him that I wanted to cut open the top and place it under a shortened gutter spout so we could collect rainwater to water the garden with it. Like-a-so:

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Obviously, my cut hole is a little crude, and I’ll likely go back and clean that up some. You may also notice that the thing is completely overflowing. Yeah. We got a little rain last night. The instant success of our water collection got me to doing some math…

The barrel is almost exactly two feet wide. Pi times radius squared gives us the area of a cross-cut on the surface of the barrel. The barrel’s radius is one foot, one times one is one, and so we can assume the area of the barrel is 3.14 square feet. Sure, I know that it would be more precise to use 3.14159265 or so, but who cares about that kind of precision anyway? Our house is just under 1,100 square feet and is pretty well bisected by the peak of the roof. the gutter runs along the full edge of the roof on that side, and has one downspout pouring into that barrel. So, we can assume that the roof and guttering system is funneling about 550 square feet of rain into our little drum, at its unknown efficiency level. The area of the roof divided by the area of the barrel ought to give us a rough multiplicative factor on how many inches of rain will fill how many inches of barrel. 550/3.14=175.16. So, every inch of rain with no loss would fill 175-inches of barrel, or about 270-gallons. Since we only have 36-inches of barrel, this tells us that one inch of rain could come close to filling up five 55-gallon drums, or 1/5″ of rain would fill up our one barrel. Last night, we got about 1.5-inches of rain, which would be enough to fill up about seven barrels the size of ours, or a collection of almost 400 gallons of water.

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Frankly, I have no idea how much water we’re dumping on our little garden, but I know the plants respond well to a good rain as opposed to tap. What I do know is that if we had a similar collection system on the other side of the house and means to actually store it, a rain like last night would have produced 800 gallons for us. This part of the state averages 36-inches annually, which translates into almost 10,000-gallons with such a collection system. Granted, I don’t think that we would rat-hole ten thousand gallons of water, as we would be using out of it between showers.

The fascination is that I’d never really thought about rain or rainfall or collecting rainwater before. I very simply had no idea that it was so easy to collect such large amounts of it. The tin-foil-hatter in me wonders how I would have to treat it and store it to effectively use it as a potable water source. For our current property, I could see having multiple barrels linked together with tubes and valves so that we could remotely fill them from the collection barrel under the gutter spout. As they filled up, we could shut them off in logical succession and water the garden from individual bottles as a cascade system. When we build, if we have established rainwater as a valuable enough resource, I could see putting in a large underground storage tank that we could direct the water to. Plus, the new place will be significantly larger than our current house. I’d say that it’s conservative to assume that we could double the reap number from what I’ve laid out above. Really, I wouldn’t go with less than a 10,000-gallon tank on new construction. Even so, the little 55-gallon rain barrel could still be valuable as an initial filtration device. Then again, we’ll be getting our tap water from a well when we build. Would there be a specific advantage to collecting and storing rainwater over letting it run off into the natural filter of the earth and pump it from groundwater as needed? I don’t know. Looks like I have homework to do there.

As I said before, I don’t really know how much water we consume by watering our garden, but I have a feeling I’m about to find out. It shouldn’t take but watering the garden from the barrel a couple times before we have some idea on that. It is turning into quite the intriguing experiment though.

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8 thoughts on “Rainwater & Gardening

  1. you’ll save a TON of money with a few barrels. we actually have one on each corner of the house and try to drain each before we turn to tap water. it’s amazing how much we use in the food plots…but if it’s grey/rainwater, i feel better knowing it’s getting used instead of simply washing away.

  2. I was stationed in Rota Spain for three years back in the early ’80’s.

    We rented a place right on the beach about 5 miles or so outside of town.

    No city water and the water table was brackish so no well either.

    The house was built with a concrete cistern under it. It was a typical Spanish flat-roofed house with a metal roof and collectors that drained the water into the cistern under the house.

    That was our potable water. No treatment necessary, just filters to remove particulates.

    I’ve heard of systems (pretty simple ones) that create a bypass to dump the first couple hundred gallons of a rainfall to flush out all the crap (literally…like bird-crap) that can collect, but we didn’t have anything like that…like I said, just filters.

    We didn’t drink the water straight from the tap, but most people don’t do that now days anyway. It was fine to cook with, we never had any problems.

    Of course if you have any industry around you that dumps chemicals into the air (shouldn’t be much of that around any more), it might be different.

    Heck, take a sample to a local university science department and have them analyze it for you. I bet they’d do it for free.

  3. Re: well vs. cistern would depend on the depth of the water table. ’round here the water table is ~110 ft. So it takes a decent size pump to get it to ground level, let alone to the house. In an off-grid system the cistern would save quite a bit of electricity.

    Re: water sample, the University here charges ~$10 per sample. Though they test for just about everything. There are also the home test kits that will get you in the ball-park.

  4. Even in water poor areas like New Mexico, I have read accounts of rainwater collection systems that have given their owners enough water to not only take them off the water grid, but allow them to also fill a swimming pool.

    I have often thought that when we have our own place of having a collection system installed just for that reason – take me of the grid.

  5. I have a well at my home, but I still use a rain barrel. I use it because the garden responds better to the rain water than to the well water. The only money I’m saving from using the barrel is probably the electricity for pumping the water up from the well, which is significant if you use a lot of water. But I bet it will take forever to make my money back because, unlike you, I spent money to buy a barrel and a gutter diverter.

  6. About the only useful comment I have is that, depending on your area, you want to be careful with open-topped pools of water laying about. ‘Round our parts, in a few days, you would have a positive flotilla of mosquitoes airborne…

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