Gravity Irrigation Systems: Easy Rain Barrel Irrigation

BlueBarrel's founder, Jesse Savou, demos her tried-and-true gravity-fed DIY drip irrigation system. Four rain barrels supply the water, and gravity does the work to keep her garden beds hydrated. Click the image to watch the video! Scroll down for more video links, including a mid-season update, and a tutorial on how to program and use a no-pressure timer.

Your rain barrels are full... so 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 we distribute the water through our garden? With a DIY drip irrigation system, of course! When we let gravity to the work, that part can be easy, too.

If you set your system up properly, you can use gravity to distribute this precious stored water. Drip irrigation is the most water-efficient way to irrigate. When you rely on gravity for distribution, it is the most energy-efficient as well.

In addition to these great efficiencies, irrigating with rainwater is wonderful because plants love the water so much. Fresh from the sky, rain is completely free of the salts, minerals, and chemicals found in other water sources. Rainwater also has the perfect pH balance and nitrate delivery to keep plants and soils healthy!

So now that your rain barrels are full, how do you get that super 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 for DIY drip irrigation systems. Learn how to irrigate with gravity!

Gravity Irrigation Systems

This article covers details of gravity-fed drip irrigation systems, and how to automate them. But first the obvious: the lowest hanging fruit is of course a watering can. Placing your spigot in a convenient location is half the battle—then just fill, water, and repeat!

In this picture, a second spigot on the BlueBarrel Rainwater Catchment System™ faces the back door of the house for easy access from indoors. Extra spigots are one of many customizations we offer.

But if you're hoping for some level of automation (and better distribution), there are easy ways to automate a gravity-fed drip irrigation system, too. Our Online Store offers a variety of options for drip irrigation kits, filters, and automated timers—all designed for low-pressure or no-pressure applications like rain barrels.

No-Kink Spigot

Add extra spigots to your system for convenience. It's easy to configure a unique set-up that works for your watering needs!


Water Flow and Distribution

The great thing about drip irrigation is that it doesn't actually require any pressure, just water in the line. Water will keep flowing downward and outward until it has nowhere else to go. That means as long as your drip line stays below the water level in your barrels, you can irrigate with gravity.

There are a couple of important considerations, though:

Basic Layout

If you have a BlueBarrel System, you can run more than one drip line if it helps you reach more of your garden. In this picture, for example, if you have a drip irrigation connection on Barrel 1 and another on Barrel 6, you can reach plants in opposite directions. And you can tee off your 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 tees and ells to create these basic layouts.

If you follow the basic principles of gravity (meaning you are not asking the water to flow uphill), these rain barrel irrigation systems are completely customizable to your garden.

Rain Barrels Drip Irrigation

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

How about distance? We used to advise that a gravity-fed irrigation system on a flat site would perform best if limited to an area of about 25' from the water source in all directions. But after years of observation, we've learned the 1/2" mainline for a drip irrigation system is broad enough that it won't constrict the flow of water. You can carry the water quite far through a 1/2" mainline, even on a flat site.

That said, you may need to limit the distance if you're including up-and-down segments, such as getting up and over into a raised bed. In theory this can be done if the water level in your barrels remains above the level of the soil you are trying to irrigate, but the ups and downs will begin to limit the distance you can distribute the water. The reason for this is you need a little extra head-pressure (a.k.a. water level) in your barrels to give the water that extra push to get up and over any lip. If you're navigating distance and multiple ups-and-downs (in and out of multiple garden beds), you'll need to experiment to see if your barrels provide enough head pressure to service your entire line.

If you have any slope at all working in your favor, you have a big advantage. (Meaning your rain tanks are uphill from your irrigation area, or the ground slopes away from your rain barrels.) The water will flow through your drip line much more freely in this case, and you'll get much greater distribution by gravity.

Max Line Lengths for Predrilled Emitterline

If you are using 1/4" predrilled emitterline to get water to your plants, you need to mind maximum line-lengths to make sure plants at the end of the line are getting water (see below).

If you are using our gravity-fed irrigation kit with inline emitters (available in our Online Store) make sure you limit your line-length as follows:

  • 6" emitter spacing: 16 feet
  • 9" emitter spacing: 22 feet
  • 12" emitter spacing: 28 feet

We also carry a gravity 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 so strict. (More on inline vs. bubbler emitters below under KEY COMPONENTS.)

EXPERT TIP: If you're working with a flat site and using pre-drilled inline dripline (recommended for veggie rows), plant the most water-loving plants closest to the water source, with more drought-tolerant plants farther away. Friction loss will cause output to 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

Keep in mind that while all drip irrigation systems are designed for low pressure, most operate on 12 - 20 PSI (pounds per square inch). A gravity fed system will only offer between 0 and 2 PSI if you are on a flat site, depending on how full your barrels are. This doesn't mean the system won't work. You will just need to leave the water on for longer to get the desired output.

set up drip irrigation filter, timer, tubing

Special irrigation timers are made for gravity-fed systems. See below for details.

For example, 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. So experiment and observe to see how much water your plants really need.

EXPERT TIP: One benefit to slower water delivery is increased saturation efficiency. So while you may expect to double your irrigation time, don't be surprised if you find an extra 5 - 10 minutes does the trick.

Natural Water Pressure and Elevation

If your barrels are elevated above ground level, you will naturally increase the amount of pressure in your irrigation system. To understand the amount of pressure you get from an elevated system, each linear foot of elevation creates 0.43 PSI.

Some folks say gravity-fed systems work most efficiently with pressure below 6 PSI (the amount of pressure created by 14' of elevation). But as long as pressure stays below the 12 - 20 PSI of standard pressurized drip systems, you should be able to get great use out of a gravity irrigation system, without requiring a pressure reducer to protect your fittings.


Bubbler vs. Inline Emitters

It's important to use non-compensating drip line for any gravity-fed drip irrigation system. Water needs pressure to overcome the tight membranes in compensating line. So if you aren't experiencing success on your first try, that's one thing to check for.

Better yet, purchase a drip kit that's designed specifically for gravity-fed applications. 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 bubbler emitters (for individual control over how much water each plant gets in an ornamental garden). Click on Tools & Accessories to see our full menu of rain barrel and irrigation accessories, and recommended uses for each kind of emitter kit. See the video below for a demo of how inline and bubbler emitters can be used together!

EXPERT TIP: Always use a fine-mesh filter with any drip irrigation system to keep emitters from clogging. We offer a streamlined irrigation filter in our online store. Its streamlined shape minimizes the pressure loss in the filter itself. 

drip emitter: inline
inline drip emitter
drip emitter for rain barrel
bubbler drip emitter

Join Jesse in the garden again to see how inline and bubbler emitters can be combined for a perfectly 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 or hedge rows. In other words, any garden layout where the hose can curve gently to serve all the plants. You can wrap a soaker hose around tree trunks for the occasional deep watering those trees so greatly need. (Not tightly around the trunk—that can lead to bark rot—but targeting the root-zone out under the tree's leaf line.)

Click the image to see a short video about irrigating with a no-pressure soaker hose! The image at right shows this garden 5 weeks after planting!

rain barrel soaker hose garden

A no-pressure soaker hose (specially for rain barrels) irrigates this brand new perimeter pollinator garden. See below for a video of how this DIY drip irrigation system is set up.

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. But as rainwater harvesting grows in popularity, special soaker hoses have hit the market just for no-pressure applications. 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 Hose

Rain barrel soaker hoses have a more porous wall, so that non-pressurized water can easily seep into your garden. The rain barrel soaker hose offers much greater distribution than a drip line. Each hose is 50 feet long and according to the manufacturer specs, two hoses can be linked together for up to 100 linear feet of distribution by gravity feed.

EXPERT TIP: Over time we've learned that rain barrel soaker hoses are prone to clogged pores. Why is this? Two primary 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. And while your garden loves the organic matter in the water, hose pores can clog over time with prolonged exposure—in other words, there's no chlorine to combat the accumulation of algae and other particulates.


So What to Do?

We've found soaker hoses perform best in the long-term when kept fully shaded. Got a dense hedge-row? The soaker hose will be perfect. Need a deep-watering aid for your trees? The soaker hose is your friend. If you put it away between uses, you won't have any problem. Even if you do lay it out in the sun, you'll be a-ok 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 drip system, always use a fine-mesh filter. Our new soaker hoses actually come with a 200-mesh filterfiner than what we recommend for regular drip systemsto help prevent clogging.

Fine Mesh Filters

Drip Irrigation Filter TeeAs mentioned (and worth repeating!), a fine-mesh filter is essential for any drip irrigation system or soaker hose, no matter the type. You may have seen the large, cartridge-shaped "Y filters" on drip irrigation manifolds. They are big and bulky and hard to miss! 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. Y-filters send the water on an off-course loop, and will reduce your already-low pressure more than you may want for a gravity-fed irrigation system. Rain Barrel Soaker Hoses need finer filtration, and they come with a 200-mesh filter that looks similar to the 100-mesh version we sell separately.

Automatic Timers

Drip systems require somebody to start the water flow. But what if you're not home (or can't remember!) to turn your water valve on and off

Automated timers offer major convenience. The only trouble is, standard irrigation timers require pressure to function properly. We've heard many stories from rainwater harvesters with a DIY drip irrigation system who set their timers and walked away proudly, only to find their rain tanks empty (and garden over-saturated!) the next morning.

Here's the kink: standard irrigation timers require a pressurized water source to close fully, so the risk is draining all of your water unwittingly.

No Pressure Irrigation Timer

Luckily industry is catching up and there are now timers on the market specifically for no/low-pressure applications. BlueBarrel offers battery-operated no-pressure irrigation timers. The timer has two simple dials, allowing the user to set frequency and duration. Set the timer and walk away for convenient automated watering.

(We used to carry a solar version of the no-pressure timer, but over time we've found these to be less reliable. Beyond that, dials were mis-labeled in a recent production run which makes them confusing to operate. We now offer only the timer we've 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 Do I NOT Need for Gravity Feed?

Typical pressurized drip systems require a few components that are simply not needed with gravity irrigation systems. With gravity, you can keep it simple and forget about these parts:

Pressure Reducers

Do I need a pressure reducer for a gravity-fed drip irrigation system? Absolutely not!

Pressure reducers (a.k.a. pressure regulators) are a key component of most drip irrigation systems. But gravity irrigation systems are remarkably simple and don't need all the parts that normal drip irrigation systems do.

Municipal water is usually pressurized to around 85 PSI. If you're using city water, a pressure reducer brings the pressure down to the 12-20 PSI range so you don't blow out your drip fittings. Of course with gravity-fed irrigation usually operating under 2 PSI (and not recommended to go above 6 PSI), you can completely forget about the pressure reducer for one less headache.

Vacuum Breakers

Do I need a vacuum breaker for a gravity-fed drip irrigation system? Again, the lucky answer is no!

Vacuum breakers (a.k.a. backflow preventers) prevent dirty water from being sucked back into the city main in the event of a pressure reversal. If you are irrigating with city water, these are very important to protect the public potable water supply.

If you are 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. Even if they did, it wouldn't create a safety issue, so you can leave the vacuum breaker out of the equation!

Click into our Online Store to view specialty irrigation gear just for gravity feed.