Low-Cost Gravity Irrigation System From A Rain Barrel

I’m an idea guy with an insatiable love of tinkering and finding better ways to do things.  I’ve built and repaired computers.  I’ve learned web design by turning my ideas into fully-functional local niche web communities.  I’ve also gotten quite good at landscaping and fixing things around the house.  But for the past five years, my garden has been the “great white whale” of my tinkering life.

We inherited a 9×16′ raised garden bed with our house, and it’s come a long way since we first started working with it.  I come from a gardening family, so having a plot of land to call my own has been an exciting prospect.  But it seems with each new thing I try, I add new hurdles to overcome.

A few years ago, we were looking to jump on the whole rain barrel water conservation bandwagon.  We found one we really liked — a Good Ideas Rain Wizard Urn 65 — and got it for a steal at Sam’s Club.  Since then, it’s been a constant struggle to find the best way to get that beloved yet stinky brown water out of the barrel and into our plants.

Going to and from the garden with watering cans is out, especially on hot summer days.  I tried just using a hose, but even after lofting the barrel a couple feet off the ground on cinder blocks, you don’t get much pressure.  Last year, I tried running a garden hose pitched downward to the garden connected to a series of weeping hoses.  While it worked at first, it wasn’t the solution I intended it to be.   The hoses kinked, the weeping hose got accidentally poked and destroyed by garden tools, and it just didn’t deliver water exactly where we needed it.

So after doing a lot of experimentation and research, I decided to try rebuilding my system with rigid piping.  I settled on CPVC, not because of any vast knowledge of plumbing but because the beige pipe wouldn’t look as funny in plain view as the stark white of regular PVC.  Once I settled on that and got all the necessary fittings and supplies I needed — the home center was visited more than once over the course of this experiment — it turned out to be stupid easy to make it work.  You can watch the video for the whole process I undertook to put the system together, but here are a few of the major takeaways:

  • Don’t cement the pipe.  Amateur plumber though I am, I chose not to cement or “glue” the pipe together more out of inexperience than design, but I’m glad I didn’t.  For one thing, you’re not dealing with a great deal of pressure with a gravity irrigation system from a rain barrel.  Simple slip fitting holds up well, even when I’ve run pressurized water from a garden hose into this system.  Not cementing the pipe allows me to change my setup at any time, to easily drain it at the end of the season, or take it down entirely if I wanted to.
  • The fittings you’ll need.  The major ones you’ll want are tees and elbows.  There are also 45-degree elbows that are nice for turning delicate corners (like around the front of the barrel).  There are also reducers, reducing tees and elbows for going from 3/4″ to 1/2″ pipe.  Get some caps too.  You’ll also want a threaded adapter to go from the spigot to the CPVC pipe.  Chances are these are normal pipe threads and not “garden hose threads,” but I found it works good enough if you wrap the male threads with teflon tape.
  • Invest in a quarter-turn full-flow ball valve for your rain barrel.  Our rain barrel came with a very basic spigot, and it has a very narrow opening for water to flow through.  I spent $10 at Lowe’s on an American Valve 3/4″ threaded model for both our barrels.  Not only does it let enough water into our system fast enough to really make this method work, but it will also fill a watering can in record time.  There are also CPVC ball valves you can install in-line in the system, but make sure they’re the “full-flow” variety to get the most out of them.
  • Buy “micro” drill bits.  The smallest bit in my drill bit pack — at least, that I could find after losing so many of them — was 1/16″, and that made too big of a hole to make this method work.  If you drill your pipe full of these holes, it will spurt a lot of water really fast at the top of the line, but it will never make it down to the end of the line.  I bought a pack of “micro drill bits” from my local home center, that had bits as small as half a millimeter.  They’re a little harder to work with, and they do break quite easily if you’re not careful, but they’ll ensure a nice steady stream of water all throughout your irrigation system.  See the video for advice on how to drill the holes to get the water to the plants.
  • Creating a “loop” helps even out pressure to all your plants.  I have 3/4″ pipe leading to my garden, with a series of reducer ports which connect 1/2″ lines that run out to the plants.  Initially I just ran the lines on either side of the garden and capped the ends, but I found that on a line with a lot of holes, pressure on the last series of holes seemed to lessen just enough to be annoying.  I ended up running a solid 1/2″ connector pipe between my two main 1/2″ lines, to create a full loop around the whole garden.  That way, enough water travels down the pipe with less holes to service the end of the busy line.
  • You will use a deceptively large amount of water.  I thought that a full 65-gallon barrel attached to a system of pipes with micro holes would mean I could water for weeks and still have water left over.  Not so much.  You’ll use a lot more than you think you will.  That’s why I built an intake into the system for a garden hose.  I can now either feed city water into the irrigation system and still deliver the same targeted watering I do with brown water, or I can also just refill my barrel with city water and continue watering like normal.  I can also feed a leader hose out of my auxiliary barrel (which we use mainly for filling watering cans) into the irrigation system if need be.  I don’t consider my rain barrel as a total replacement for city water.  I use brown water when I have it, and continue with the city water when I don’t.
  • Watering timers don’t – for the most part – work for rain barrels.  I really wanted this to work for me, but it didn’t.  Last year, we went on vacation for a week and I wanted to get a battery-powered timer for the rain barrel.  If you get one, it has to say it’s made for a low-pressure or rain barrel situation, and I haven’t found many that are (at least in any sort of affordable realm).  If you just go to Walmart and buy a hose timer off the shelf, it will only drip a pencil-thin stream of water from the spigot.  I just don’t think it’s worth the trouble.  Go out and water the garden yourself, or (gulp!) make friends with your neighbor and ask them to irrigate your garden while you’re away.
  • One minor possible flaw in this system.  You wouldn’t think it, but those micro drill holes in your lines can clog.  When it rains on our garden, dirt does splash on the pipes and it can get into the hole and clog it up.  If you don’t do a good job at screening the water entering your rain barrel, you can also introduce debris into your system that you may have to flush out from time to time (leave a cleanout spot at the bottom of your system like I have in my vide0).  So far it hasn’t happened to me enough to be a “tear the whole damn thing out” situation.  Every once in a while, I may have to go in with a drill bit by hand and poke open a clogged hole.  Sometimes even brushing your finger over the hole will open it up.  If you run a city water hose into your system, you can also increase the pressure a little to blow it open.  Just be careful not to put too much on the system or you may blow apart a slip fitting or two.  Whatever you do, don’t be tempted to make the hole bigger.

Feel free to leave comments and questions below.  This isn’t a perfect system, but it’s a great way to target water directly to the plants and not oversaturate the garden.  It’s a great way to harvest and use brown water, which is free of all the chlorine and God knows what else that’s in city water.  Give it a try!  I hope it works for you.

Summary
Low-Cost Gravity Irrigation System From A Rain Barrel
Article Name
Low-Cost Gravity Irrigation System From A Rain Barrel
Description
In this article and video, I show you how I built an effective, low-cost gravity irrigation system for a garden using a rain barrel and CPVC pipe.
Mark David Zahn

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