Demystifying Downspout Diverters for Rain Barrels

As a rainwater catchment company, we answer lots of questions about the downspout diverter for rain barrels. Just how do you get water from your roof into a rain barrel (or a series of them), anyway?

The BlueBarrel Rainwater Catchment System™ provides a top-to-bottom (roof to barrel, that is) solution for harvesting and storing rainwater.

This article covers our standard downspout diverter, demystifying how it works. We'll also cover some alternatives, for those who are thinking:

"What if the standard solution won't work for me?”

A quick breakdown: On the average building, rainwater cascades down the roof and into gutters, which run horizontally to capture water from the roofline. Then, water courses through a number of downspouts, the vertical elements that carry roof runoff to the ground. Without rain barrels, this water usually makes its way into a storm drain, or is piped away from the building onto the landscape.

Rain barrels allow you to divert this water and store it for beneficial use. This has environmental benefits both in terms of water conservation and stormwater mitigation.

BlueBarrel's Standard Downspout Diverter

The BlueBarrel System uses a Flexi-Fit downspout diverter. This nifty piece intercepts rainwater flowing through a downspout and redirects it into a linked system of barrels. Once the barrels reach full capacity, the diverter redirects the flow back down the existing downspout.

After 10 years in business (and longer for R & D!), this is the downspout diverter we like best, especially for a multi-barrel system like the BlueBarrel System. Here’s why: 

It’s easy to install:

EarthMinded Flexi Fit Downspout Diverter for Rain BarrelsThe rubberized diverter head is flexible. It inserts into standard downspouts with a simple hole, and no need to cut your downspout. 

We carry versions fitted for standard 2 x 3” and 3 x 4” rectangular downspouts, and also for round downspouts between 3” and 4” in diameter. The rubber diverter head seals on the inside of the downspout. Water collects in an interior reservoir and is swiftly delivered through the inlet hose and into your tank or barrel(s). 

It handles overflow automatically, and optimizes the inflow rate:

“But what about that big hole in the middle?”

Ah, there’s another common question. The most brilliant thing about this diverter is that it optimizes inflow to fill rate, and handles system overflow automatically. Because of that hole, this is all possible with no on-and-off switch. It’s a true “set it and forget it” solution.

If your barrels have any capacity at all, water will flow in. When they are full, it will flow down as if they weren't there. This is an easy and automatic way to keep barrels topping up even as you use the water.

When installed correctly (with the inlet hose completely level), a full barrel will cause water to back up in the hose. Once the water column starts rising in the downspout, excess flow falls down the middle to exit your downspout as it would if your barrels were not there. 

This adds major convenience because you don't even need to think about system overflow. While there are plenty of ecological overflow solutions you can pursue when you have time, rest assured that you will not be creating any new drainage problems when you install a basic BlueBarrel System.

a downspout diverter
Our standard diverter connected to a downspout (with a Leaf Eater installed above it).

How does the downspout diverter capture enough water with the hole in the middle?

First, it's important to understand how water flows through a downspout to begin with. Many people imagine stormwater coursing through the gutters and free-falling down the downspouts, but that's not how it happens. Surface tension actually causes water to hug the interior walls of the downspout as it exits.

(Have you ever tried to pour water slowly from one container to another, only for it to run down your arm and drip from your elbow? That's the same effect. The water hugs the surface, whether it's your arm, or a downspout!).

So most water will be delivered directly to the reservoir at the edge of the diverter head. Only when rainfall volumes exceed the inflow rate of the inlet hose will you start see simultaneous overflow: another important concept that we'll help you understand.

Demystifying Simultaneous Overflow:

In heavy rains, you may notice water is entering your system and exiting the bottom of the downspout at the same time. You can double check to make sure the downspout diverter head is installed correctly (with a level inlet hose and not crimped inside the downspout), but otherwise, this is how the piece is designed to work.

If water enters the system faster than it can move through the pipes that connect all the barrels, you will end up with backup. This can lead to uncontrolled overflow, which can be a big problem.

So simultaneous overflow could also be thought of as balanced inflow. That sounds better, doesn't it?

How hard does it have to rain before we see simultaneous overflow?

That depends on the size of your rooftop. The smaller your collection surface is, the harder it has to rain before you'll see simultaneous overflow. If you’re collecting from a very large surface, you may see simultaneous overflow with just moderate rains.

TWO DOWNSPOUTS
This (beige) BlueBarrel System taps into two downspouts for a faster fill.

Is Simultaneous Overflow Bad?

We don't think so! Simultaneous overflow allows inflow and overflow to be more balanced throughout the season. Your storage tanks have the ability to collect a certain amount of water. Excess water will overflow regardless, so by optimizing the inflow rate, overflow exits at lower rates over a longer period of time. This increases your ability to infiltrate this water onsite, which is what you really want for the best ecological design. 

That said, we do have a few suggestions for how to increase inflow for faster fill. First, just remember a multi-barrel system like the BlueBarrel System can't fill any faster than water can get through the connection lines. While there are some creative ways to increase the rate of transfer between barrels, in a standard setup, the most sound approach is to match the inflow rate to the rate at which the system can fill. Otherwise you will create backup issues.

This usually means you want to allow some simultaneous overflow when rainfall volumes are excessive. Overflow is much easier to manage at lower and more consistent rates. 

But there are many ways to increase inflow without creating overflow issues. The system above, for example, collects from two separate downspouts: one at each end of the system. The BlueBarrel System is very flexible in this way. Our interactive online store allows you to choose all kinds of customizations, including extra diverters, so you can feed a single system from multiple downspouts.

The picture below shows another creative approach. The first diverter is installed higher than the second. The lower diverter will catch overflow from the higher one in heavy rains. But again, for a small system, there is such a thing as too-much/too-fast, so the RainRouter Selector Valve on the bottom diverter allows the user to send excess water through a hose to direct it elsewhere. (RainRouters are available in our online store as well).

double diverter set up
This customer installed a second diverter to capture overflow from the first.

Still, many folks contact us about cutting the downspout to divert all flow into the rain barrel. While it’s common to want to fill the barrel as quickly as possible, unless you have large tanks, this is usually not the best design solution. Diverting all water into a barrel requires a separate overflow (we’ll go over that below), and your system will fill so quickly that all excess water will overflow at sometimes-higher-than-manageable volumes.

In most cases, a more balanced inflow solution with automatic overflow handling makes the most sense. Review the double-diverter strategies above for balanced ways to increase inflow while still benefitting from the automatic overflow function.

What if My Downspouts are Not Compatible?

In our online store, we carry diverter heads for 2 x 3" and 3 x 4" rectangular downspouts, and round downspouts between 3" and 4" in diameter. This covers most standard residential and industrial sizes.

Do you have a different size, or maybe a completely different roof drainage system like rain chains or scuppers? No need to worry. We have a surprisingly simple solution: 

Leaf Eater as Adapter

A Leaf Eater is a standard upgrade to any rainwater system, and is highly recommended for keeping leaves, mosquitoes, and other debris out of your rain barrels or tanks in any case. Also known as a debris excluder, it is one of our most popular accessories

The great thing about the leaf eater is it adapts to any of the standard sizes listed above—round or rectangular! Installation, while simple, does require a clean cut to the downspout. This is a good thing if you have non-compatible downspouts, or no downspouts at all.

Water free-falls onto the leaf eater, so it doesn't matter what dimension you have above it. Downspout material is very inexpensive and you can replace your lower segment with, for example, 2 x 3" downspout material for a standard diverter connection, as shown in the video. 

While we don't love the idea of plastic in general (except for re-used of course!), plastic downspout material is a low-hanging fruit in this case. It is inexpensive, easy to cut, and seals very well against the rubberized diverter head. 

In fact, the "leaf eater-as-adapter" solution is so effective, it really matters not what's going on "upstream" of the leaf eater, as long as you can funnel water onto the screen in one way or another. 

Rain chains can be cut to release onto a leaf eater. Leaf eaters can be installed to catch water from a scupper, or a makeshift drainage. The options are limitless!

leaf eater as adpater options
Non-standard downspouts? Simply direct your roofwater onto a Leaf Eater to adapt!

What if I Still Want to Set Up a Full-Diversion Solution?

You certainly can. In general, this is not a proportional approach for smaller systems like single rain barrels, or even linked rain barrel systems, for the reasons described above. But it may be a good idea for larger tanks. 

Whether your tanks are large or small, for proper ventilation and overflow handling, you need to have an overflow equal to or greater in size than the sum of all inlet ports. To make that simple, if you have a 3" inlet, you need a 3" overflow on the same vessel.

Imagining this on a 55-gallon rain barrel, you begin to understand how the overflow port takes a significant bite out of your storage capacity. Multiply that loss for a multi-barrel system. In addition to uncontrolled overflow, this is another reason full diversion is usually not recommended for smaller systems.

The other thing you need to consider is where to direct that overflow. While a prefab diverter handles overflow automatically by design, a custom-crafted full-diversion will need to be paired with careful consideration of overflow management.

Consider that overflow rates will be irregular and sometimes very high. Direct overflow to an infiltration basin at least 15' from any structures, or to another place where it can safely infiltrate. 

Custom Downspout Diverter
"I thought the instructions with the BlueBarrel DIY RainKit were well written and easy to follow. I made one adjustment that I thought I would share. I built a trellis to extend my catchment area and used a 2" ABS drain pipe to the barrels. A 2-1/4" kitchen strainer fits perfectly between two MIP and FIP couplings."
- Robert | San Luis Obispo, CA

This BlueBarrel customer created his own inlet. A separate overflow of at least the same size will be required, to route excess water to a safe drainage spot.

What if I Don't Have Gutters or Downspouts at All?

The simple answer is you would need to install them. But not necessarily. What you really need to do is gather your water into a single location so that it can be collected. Really, as described above, all you need to do is get the water onto a leaf eater in one way or another.

Check out the Occidental Arts & Ecology Center's (OAECs) Wonder Gutter solution for one very inexpensive way to create your own gutter system!

What if I Don't Have a Roof?

In comes the rainwater funnel. Rainwater harvesting works because the roof serves as a collection surface, catching a large volume of water and (usually) funneling it through a series of gutters and downspouts. This concentrates the water for easy collection. 

Can't I just put an open barrel in a field?

Sure, but if you get one inch of rain, you'll have exactly one inch in the bottom of your barrel... until it starts evaporating! This is the beauty of the collection surface: That same inch of rain falling on a modestly sized 1,000 square foot rooftop will generate over 600 gallons of high-quality rainwater. That's enough to fill 11 standard 55-gallon rain barrels, to put things in perspective. 

Even a very small surface, like an 8 x 8' garden shed, will fill a 55-gallon barrel with less than 1.5" of rain. If you don’t have any outbuildings to collect from, you can create a modest increase to your collection surface with a rainwater funnel.

While it won't give you the kind of surface area even a very small rooftop would, the funnel can increase your surface area 2-3 times or more. This may be a useful solution for open-field watering needs like livestock, birdbaths, establishing orchard plantings, or habitat restoration

rain barrel with rain saucers
No roof? No problem! You can outfit your barrels with a funnel, a.k.a. "rain saucer"!

Consider installing a small outbuilding, or even a shelter to shade your storage tanks. Some folks have installed free-standing solar panels in the middle of a field and collected from those. Solar panels have high collection efficiency, and provide other ecological benefits as well. Wouldn't it be useful to have some shade or storage (or energy production!) out next to your stored water anyway?

With this in-depth primer, we hope you're ready to start harvesting, no matter what kind of downspouts you're starting with. Step through our online planning tools to customize a rainwater system for your place, and feel free to contact us with questions. We're here to help!

 

Article by Jesse Savou, MA Ecological Design, ARCSA/ACCE Certified Rainwater Harvesting Professional

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