BlueBarrel founder, Jesse Savou, demos her gravity-fed DIY drip irrigation system. Four rain barrels supply the water, and
gravity does the work to hydrate her garden beds.
Your rain barrels are full. Now what?
Rainwater harvesters know how fast and easy it is to fill a series of rain barrels from the roof. But once those barrels are full, how do you distribute this precious stored water through the garden? With a gravity-fed drip irrigation system, of course! When you let gravity to the work, that part can be easy, too.
Drip irrigation is the most water-efficient way to irrigate. When you rely on gravity for distribution, it is also the most energy-efficient.
Irrigating with rainwater is wonderful because plants love the water so much. Fresh from the sky, rain is free of the salts, minerals, and chemicals found in other water sources. Rainwater also has the perfect pH and nitrate delivery to keep plants and soils healthy.
Now that your rain barrels are full, how do you get that high-quality water over to your thirsty garden?
Rain barrels aren't pressurized like municipal water, so getting the water from here to there takes a little thought. This article offers tips and tools to use gravity for DIY drip irrigation system.
Gravity Irrigation Systems
This article covers gravity-fed drip irrigation systems, and how to automate them.
It is easy to irrigate with gravity, if you understand a few key principles. Our Online Store offers a variety of options for drip irrigation kits, filters, and timers—all designed for low-pressure or no-pressure applications like rain barrels.
Placing your outlets in a convenient location is half the battle—then just fill, water, and repeat!
Add extra outlets for convenience. It's easy to configure a unique set-up that works for your watering needs.
In the photo above, a second spigot on the BlueBarrel Rainwater Catchment System™ faces the back door of the house for easy access from indoors. A ground-level drain valve exits the far end of the system to feed a Rain Barrel Soaker Hose. This system is featured with more videos below.
High-Flow Drain Valves are now provided standard with our DIY RainKits™, which connect at ground-level to fully drain all barrels through a gravity-fed irrigation system. As described below, multiple drain valves can be used on larger systems to extend your irrigation area in all directions.
A DIY GUIDE TO GRAVITY IRRIGATION: KEY CONCEPTS
Water Flow and Distribution
The great thing about drip irrigation is that it doesn't require any pressure, just water in the line. Water will keep flowing downward and outward until it has nowhere else to go. As long as your drip line stays below the water level in your barrels, you can irrigate with gravity.
There are a few important considerations, though:
High-Flow Valves
While gravity will distribute water until it has nowhere else to go, you can help keep things flowing by using valves and fittings that restrict water flow as little as possible.
A standard 3/4" spigot or drain outlet has 3/4" threads on it, but the gate-valve inside has a much narrower opening, often less than half an inch.
Use High-Flow Spigots and Drain Valves to head off your gravity-fed irrigation system with strong flow. Originally available as an upgrade, these high-flow valves are now included standard with our DIY RainKits™, and available for individual sale from our accessories menu.
Read below about our Streamlined Drip Irrigation Filters—another specialty product that allows for better flow than its standard alternative.
Basic Layout
With a BlueBarrel System, you can run more than one drip line to reach more of your garden. In this picture, for example, there is a drip irrigation connection on Barrel 1 and another on Barrel 6 to reach plants in opposite directions. Tee off the main lines to service the entire area in between using a grid or "fork" pattern. The gravity-fed irrigation kits available in our Online Store include fittings to create these basic layouts.
If you follow the basic principles of gravity (meaning you are not asking the water to flow uphill), rain barrel irrigation systems are completely customizable to your garden.
This 6-barrel System irrigates a water-wise garden with gravity-fed drip irrigation. The gentle slope towards the sidewalk allows for great distribution through the drip line, and adjustable bubbler emitters allow the user to control how much water each plant gets.
Slope, Distance and Raised Garden Beds
We used to advise that a gravity-fed irrigation system on a flat site performs best when limited to an area of 25 feet from the water source in all directions. But after years of observation, we learned that the 1/2" mainline is broad enough to not constrict the flow, carrying the water quite far, even on a flat site.
You may need to limit distance to include up-and-down segments, such as getting into a raised garden bed. Raised beds can be irrigated by gravity-feed if the water level in your barrels remains above the soil you are trying to irrigate, but ups and downs will begin to limit the distance you can distribute water. This is because you need a little extra head-pressure (water level) in your barrels to give the extra push to get over any lip. If you're navigating a distance with multiple ups-and-downs, you'll need to experiment to see if your barrels provide enough head-pressure to service your whole line.
If you have a slope working in your favor (rain barrels are uphill from the irrigation area, or the ground slopes away from your barrels), you have a big advantage. The water will flow through your drip line much more freely with greater distribution.
Max Line Lengths for Predrilled Emitterline
If using 1/4" predrilled emitterline, (like our Gravity-Fed Irrigation Kit with Inline Emitters, or the emitterline sold individually in our Online Store), mind maximum line-lengths to make sure plants at the end of the line are getting water. Limit your line-length as follows:
- 6" emitter spacing: 16 feet per row
- 9" emitter spacing: 22 feet per row
- 12" emitter spacing: 28 feet per row
We also carry a Gravity-Fed Irrigation Kit with Bubbler Emitters. Bubbler emitters punch directly into the 1/2" irrigation mainline, and the ones we sell are individually adjustable for flow, so the distance restrictions are not as strict. (More on inline vs. bubbler emitters below under KEY COMPONENTS.)
EXPERT TIP: If you're on a flat site and using pre-drilled emitterline (recommended for veggie rows), plant the most water-loving plants closest to the water source, a more drought-tolerant plants farther away. Output will decrease farther down the line, so account for this in your planting. (Watch our mid-season update video for more detail.) If you're using our custom-punch bubbler emitter kit (see below), you can twist each emitter to control the flow based on individual plant-needs. This is what we recommend for ornamental gardens.
Watering Time
While all drip irrigation systems are designed for low pressure, most operate on 12 - 20 PSI (pounds per square inch). On a flat site, rain barrels produce only 0 - 2 PSI, depending on how full they are. But remember, drip irrigation doesn't require any pressure, just water in the line. If you follow the principles of gravity feed outlined in this article, you can irrigate with this very low pressure. You will just need to leave the water on for longer to get the desired output.
Special irrigation timers are made for gravity-fed systems. See below for details.
Your drip line may have a 1 GPM (gallon per minute) rating, but a gravity fed line will take longer than a minute to emit one gallon. Experiment and observe to see how much water your plants really need.
EXPERT TIP: One benefit to slow water delivery is increased saturation efficiency. While you may think you’ll need to double your irrigation time, an extra 5-10 minutes may do the trick.
Natural Water Pressure and Elevation
You can naturally increase the amount of pressure in your irrigation system if your barrels are elevated, or placed above the soil level you are irrigating. Each linear foot of elevation creates 0.43 PSI.
Gravity-fed irrigation systems work most efficiently with pressure below 6 PSI (the amount created by 14' of elevation). But as long as pressure stays below the 12 - 20 PSI of standard pressurized drip systems, your gravity irrigation system will distribute water to your garden without any need for a pressure reducer to protect your fittings.
A DIY GUIDE TO DRIP IRRIGATION: KEY COMPONENTS
Bubbler vs. Inline Emitters
It's important to use non-compensating drip line for gravity-fed drip irrigation. Water needs pressure to overcome the tight membranes in compensating line. If you aren't experiencing success with the equipment you already have, that's one thing to check for.
BlueBarrel stocks two plug-and-play options for gravity-fed drip irrigation in our online store: one with inline emitters (for vegetables and row crops), and one with individually adjustable bubbler emitters (to control how much water each plant gets in an ornamental garden). Go to Tools & Accessories to see our full menu of supplies, and recommended uses for each kind of emitter kit. (The video below demonstrates how inline and bubbler emitters can be used together.)
EXPERT TIP: Always use a fine-mesh filter with a drip irrigation system to keep emitters from clogging. We offer a Streamlined Drip Irrigation Filter in our online store. Specifically made for gravity-feed, its streamlined shape minimizes pressure-loss within the filter.
Join Jesse in the garden again to see how inline and bubbler emitters can be combined for a customized gravity-fed drip irrigation setup.
Soaker Hoses
Soaker hoses have a porous surface that allows controlled amounts of water to seep out as water flows through. Weave a soaker hose through your garden and water will sink into the soil along the length of the hose.
Soaker hoses work wonderfully for perimeter gardens, hedge rows, or any layout where the hose can curve gently to serve every plant without a lot of exposure in between.
You can wrap a soaker hose around tree trunks for the occasional deep watering that trees need. (Not tightly around the trunk, which can lead to bark rot, but targeting the root-zone under the leaf line.)
Click the image for a short video about irrigating with a no-pressure soaker hose. The next image shows this garden 5 weeks after planting!
A no-pressure soaker hose (specially for rain barrels) irrigates this new perimeter pollinator garden. See below for a video demoing how to set up a system like this.
What's Special About the Rain Barrel Soaker Hose?
Like drip irrigation lines, most soaker hoses are designed to work optimally with certain amounts of pressure. As rainwater harvesting grows in popularity, special soaker hoses have hit the market. BlueBarrel is proud to be one of the few vendors that offers No-Pressure Soaker Hoses specifically for rain barrels and rain tanks.
Rain barrel soaker hoses have a more porous wall so non-pressurized water can easily seep into your garden. Each hose is 50 feet long, and two hoses can be linked together for up to 100 linear feet of gravity-fed distribution.
EXPERT TIP: Rain barrel soaker hoses are prone to clogging for two reasons: (1) The pores are larger to compensate for non-pressurized water. This lets a little bit of sunlight in, which leads to algae growth. (2) One of the major benefits of irrigating with rainwater is that it isn't chlorinated. While your garden loves the organic matter in the water, hose pores can clog with prolonged exposure because there's no chlorine to combat the accumulation of algae and other particulates.
So What to Do?
In the long-term, soaker hoses perform best when kept fully shaded. Got a dense hedge-row? The soaker hose is perfect. Need a deep-watering aid for your trees? The soaker hose is your friend. When put away between uses, you won't have any problem.
If you do lay it out in the sun, you'll be fine for quite a while. When you start to notice the output decline, flush out the pores with a blast of pressurized water.
As with a standard drip system, always use a fine-mesh filter. Our Rain Barrel Soaker Hoses come with a 200-mesh filter—finer than the filters we sell for our Gravity Fed Drip Irrigation Kits—to help prevent clogs.
Fine Mesh Filters
It is worth repeating that a fine-mesh filter is essential for any drip irrigation system or soaker hose. You may have seen large, cartridge-shaped "Y filters" on drip irrigation manifolds. They are bulky and send the water on an off-course loop, reducing the pressure more than you may want for your gravity-fed irrigation system.
For gravity-fed drip irrigation, we recommend a 100-micron Streamlined Drip Irrigation Filter. These are less expensive than Y filters, much smaller and sleeker (a.k.a. better looking!), and they keep the water on a streamlined course to your drip-line.
Automatic Timers
Drip systems require somebody to start and stop the water flow. But what if you're not home, or forget to turn your water valve on and off?
Automated timers offer major convenience. But there's a catch: standard irrigation timers require pressure to fully close. We've heard many stories from rainwater harvesters who set their timers and walked away, only to find their rain tanks empty and garden over-saturated the next morning.
Thankfully, there are timers made specifically for no- and low-pressure applications. BlueBarrel offers battery-operated no-pressure timers. The timer has two simple dials, allowing the user to set watering frequency and duration and then just walk away. (We used to carry a solar version of the no-pressure timer, but over time these proved to be less reliable. We now offer only the timer that we found works best.)
Watch our quick video tutorial on how to program and use this amazing no/low-pressure timer!
With these great new products available to help automate non-pressurized tanks, it's now much easier to irrigate with collected rainwater in your garden!
What Parts Don't I Need for Gravity Feed?
Typical pressurized drip systems require a few components that are not needed with gravity irrigation systems:
Pressure Reducers
Pressure reducers (a.k.a. pressure regulators) are a key component of pressurized drip irrigation systems. Municipal water is usually delivered at about 85psi. When using city water, a pressure reducer brings PSI down to the 12-20 range so you don't blow out your drip fittings.
With gravity-fed irrigation systems operating well below that, you can completely forget about the pressure reducer.
Vacuum Breakers
Vacuum breakers (a.k.a. backflow preventers) prevent dirty water from being sucked back into the main in the event of a pressure reversal. Irrigating with city water, these are important to protect the public drinking water supply.
When irrigating from rain barrels or tanks, you should not have a cross-connection with the municipal water system. There is no risk of your rain barrels sucking the water back in.
