I maintain eight 55-gallon rain barrels around my house, six of which I use to water my garden.
I used to pat myself on the back for doing my part for the Chesapeake Bay, by installing and maintaining those rain barrels. Those barrels reduce runoff into the bay, and runoff is the principal source of the nitrogen and phosphorus nutrient overload in the Bay. (Those nutrients dissolved in rain water come from air pollution, mostly from cars and power plants. This is why reducing storm water runoff has been a principal focus of Chesapeake Bay Preservation Act. See my post on bioretention for a quick overview of all that.)
Then I made the mistake of doing the math (Post G21-043, shown above). As you can see from the right-hand column on the table above, my rain barrels, fed by about 850 square feet of roof area, are a drop in the bucket (far right column). The six-barrel system for my garden diverts just 0.6% of the rain that falls on my yard. Their impact on runoff is more-or-less rounding error.
The other odd aspect of rain barrels, shown in the table above, is that they are characterized by strongly diminishing returns. Above, I used actual local weather data to model an idealized 300-square-foot garden, watered by six 50-gallon barrels fed by 850 square feet of roof. (Details are in Post G21-043). For that setup, in Virginia, the first two rain barrels halve your use of municipal water for watering the garden. Each year, those two barrels would save me a bit over $17 in municipal water and sewer costs. The first two barrels plausibly they pay for themselves over their useful lifetime. (Mine are recycled soda-syrup barrels, some of which are now in their their third decade of use as water barrels).
But the same model (850 square foot roof area, 300 gallons of barrels, 300 square foot garden, Virginia weather) shows that going from 10 barrels to 20 saves just over $2.50 in additional municipal water cost per year. The un-discounted payback period for those barrels would be measured in centuries.
And that, in turn, is a fundamental aspect of the weather in this area: When it rains, it pours. If we’re getting consistent weekly rains, I don’t need the barrels, and they sit full. But one hot summer week with no rain will drain them completely. If I want to extend their useful life to two weeks of drought, I need another six barrels. Which then are more-or-less idle for an even greater portion of the summer than the first six are.
Dual-pressure irrigation system? Nope, use Theorem 1.
One thing that I am absolutely sure about, regarding rain barrels, is that I’m really tired of toting buckets and cans of water around. To put one inch of water on (say) 300 square feet of raised beds, that’s 187 gallons of water that I must tote from the rain barrels to the garden.
I bought a small submersible pump for those days when I don’t much feel like carrying dozens of five-gallon buckets of water. But it’s slow, particularly when attached to the length of hose required to get to the far reaches of the raised beds. So that’s less effort, but it’s still takes a lot of time.
And this year, I’ll be growing parthenocarpic cucumbers and zucchini (Post G22-013) under insect netting. So I’ll have one bed where an irrigation system is almost a must. I don’t want to have to pull back the netting every couple of days in order to water that bed in the heat of summer.
In any case, after two years of toting buckets during the hottest part of the summer, this year I’m installing a drip irrigation system.
Up to now, I hesitated to do that, because:
- I wasn’t sure if I was going to keep gardening after the end of the pandemic.
- It seemed like a lot of bother for a few square feet of garden.
- Buckets and watering cans work, and are good exercise.
- This means bringing yet more plastic into my garden, which means disposing of that plastic, once UV-deteriorated, some years from now.
- Undoubtedly the only parts I can get will be Made in China.
But mostly it was because:
- I had no clue how to make that work.
In particular, I use both water barrels and municipal water to keep my garden going (per the table above). I need a system that will work with both water sources. It has to work with the nearly-zero water pressure of a gravity-fed rain barrel system, and with the (possibly reduced) pressure from the town water mains.
That, plus general ignorance of the topic, was enough to keep me schlepping pails of water for the past two years.
But after reading up on this, and filling up and abandoning a lot of on-line shopping carts, I think I finally know enough to cobble together a system that will work for me.
The first key realization is that almost nothing designed for a normal (that is, pressurized) irrigation system will work well with a low-pressure water-barrel system. Without going into detail, some stuff (e.g., “pressure-balanced” anything) literally won’t work. Other things might or might not work, depending on the specific parts that I buy.
And the reverse is also true. A tame drip at 1.5 PSI becomes a sprinkler at 25 PSI. Or simply blows apart the various hose couplings at that pressure. And the likelihood that I can use one set of pipes to achieve a balanced flow at 1.5 PSI and 25 PSI seems pretty low.
The second key insight sounds stupid, but it took me about two years to figure this out. I kept thinking that I needed a system that could work with either rain barrels or municipal water (with some sort of pressure reducer). At some point, I even considered putting in two parallel systems, which would be a lot of work and wasteful to boot.
Have you figured out the simple solution yet?
I don’t need to run this at two pressures. I can just fill the rain barrels with municipal water, and use one low-pressure irrigation system for both rain water and municipal water. (I run the municipal water through a charcoal filter to remove chloramines before I use it.)
This is what is known in my family as “put the kettle on the floor and use Theorem 1”. It comes from an old joke about asking a mathematician how to make tea, starting with a cold, empty tea kettle sitting on the floor. (Take it off the floor, fill it, put it on the stove, heat it to boiling, pour it over tea leaves). When asked how to make tea, with a kettle full of boiling water sitting on the stove, the mathematician’s answer was to empty the tea kettle, put it on the floor, and use Theorem 1.
The way to eliminate the need for a dual-pressure irrigation system is to take that nice, clean, treated, expensive city water, and put it into my less-than-pristine old rain barrels. Once you get over the shock of that, it all makes sense. That way I can distribute that water through the existing and (hopefully) fine-tuned low-pressure irrigation system. And there’s no need for a pressurized water irrigation system at all.
I can’t believe it took me two years to realize that.
KISS
Irrigation systems using pressurized water are pretty much point-and-shoot affairs. Run some tubing of a reasonable diameter, and then almost any type of “emitter” will work. Anything from soaker hose to sprinkler heads to whatnot.
By contrast, a low-pressure irrigation system — gravity-fed from rain barrels — is more of a one-off piece of engineering. You only get about 0.5 PSI per foot of elevation. You might have, at best, one or two PSI of pressure, to run the entire system.
For sure, there aren’t going to be any sprinkler heads in my system.
Even with that limitation, it’s easy enough to use a rain barrel to irrigate a single plant or small area. Right now, I have a potted lime tree hooked up to the nearest water barrel, via a filter, timer, and a garden hose with some nail holes punched in it. The filter keeps the junk in the barrel out of the timer. The timer periodically opens a valve to let the water flow. And when it does, the plant gets a gentle sprinkling of rain water around the circumference of the pot, for a minute or two.
Want more water? Hammer in a few more nail holes, or leave the timer on longer. It’s straightforward. Idiot-proof, even,
Doing a larger area is far more complicated. You want to get uniform water distribution over a large area, but the water pressure drops the further you are from the water barrel, or the higher the elevation of the raised bed. Nail holes in a garden hose just won’t cut it.
In addition, most parts designed for pressurized irrigation systems won’t work on a gravity-fed rain barrel system. Most sprayers, bubblers, emitters, drippers, timers, and so on are designed to work with a minimum of maybe 10 PSI. There are some bubblers made for low-pressure systems. But (e.g.) anything that says “pressure compensated” likely won’t work for a rain-barrel system, because they pressures they have in mind are far higher than what a gravity-fed system can achieve.
Given all the uncertainty, I’m just going to buy tubing, and poke holes in some of it, in a fairly systematic way. No bubblers, emitters, sprinklers, soaker hoses, and so on. Just tubing, with holes poked in it. I think that’s about the limit of what I’ll be able to understand.
Plus, that’s about the cheapest way to go about this. One roll of 1/2″ tubing to delivery water down the length of each bed, then 1/4″ tubing (with holes in it) to drip the water into the bed. A filter, some fittings, and a hole punch should be about all I need.
It looks like the process of setting up one of these is reasonably idiot-proof. If you don’t have enough water, make more holes in the pipe. If you have too much water, plug the holes with “goof plugs” sold specifically for that purpose. Keep the runs of pipe as short as possible, use larger pipe (1/2″) to deliver water along the bed, and smaller pipe (1/4″) with holes to drip the water into the bed.
In the end, it’s not rocket science. Water flows downhill. I just have to give it a way to get from the barrel, to the raised bed, in a controlled fashion. The trick is to avoid all the fancy stuff that works with pressurized systems, and to realize that nothing bars me from running municipal water into my water barrels, and from there, through my low-pressure irrigation system.
I’ll let you know how things work out.
