open-source rainwater catchment methods and kits

portland, oregon
We are all Makers. We believe in Open Hardware
. If something is truly for the greater good, it is not a secret. We are compelled to publish the methods of collecting, delivering and building rainwater-related catchments that we think folks should know about (including the ones we offer for sale)... Sometimes we hope you buy a kit from us, and other times we hope you'll try and Do It Yourself. In fact, we'll help you either way.


Contain Rain "Water-Arm" (intake + overflow) APPROVED
The Garden Watersaver™ (intake + overflow) APPROVED*


Bottom-Link / Top-Vent APPROVED


3/4" Spigot / Drain / Hose (+Drip Irrigation) APPROVED
Self-Hydration / Soil Wicking APPROVED
Electric Pumps (AC/DC) TESTING
[Please note: These illustrations are concept-proofs intended to describe the flow of water and air through a system; they do not reflect final system/kit design. For complete systems, see our kits page.]

Intake + Overflow

The Garden Watersaver

Intakes & Overflows

What is an intake and what is an overflow?

An intake is simply where the water enters the system. An intake could have a filter and a hose attached to it, or it can just be a hole. An overflow is the method used to deal with excess water after the system has filled. It is often referred to as a diverter. These two points can be combined in some methods and separate in others. We prefer combining them, as it is a more elegant solution. More time is given to this point below.

What is the Contain Rain Water Arm?

The Water Arm is Contain Rain's custom water diverter. It is made with 80% reclaimed material. It acts as both a water intake, filter, and overflow system. The purpose of the Water Arm is to send incoming water to the rain barrel until it fills completely. Once the barrel is filled, water backs up through the attached hose, filling the main chamber and is then diverted out the 2-inch-diameter "arm" and back into your downspout. With some tin snips and a screwdriver, you can easily install the Water Arm into your downspout. Click here for a visual illustration of how the Water Arm works.

What's the distinction between the Water Arm and the Garden Watersaver?

The Garden Watersaver is a good product; it handles intake and overflow adequately. It has a low profile, and is easy to install. However, we've encountered some issues, particularly that: The Garden Watersaver hose slips off easily (especially in summer conditions), there is no supplied connector (hose barb) to attach it to a barrel, and it depends on 100% fabrication of new materials through injection molding. It is also made outside of the United States, and it is quite expensive ($30+ MSRP).

Because of the fragile net environmental gain of collecting rain in barrels, we have invented the Water Arm to address these issues. The Water Arm hose fits so snugly you'll need two body builders to take it off (well, not really). The Water Arm is made from almost all reclaimed material, therefore reducing demand for new plastics and lowering the price! Our design for the Water Arm is available as open-source (open-hardware), so you (yes, you!) can make your own. (But you might find that ours is less expensive anyway.) The Water Arm is even easier to install than the Garden Watersaver (if that were even possible!) because it requires no specialized angled cuts. We still carry the Garden Watersaver (at $10 less than MSRP) alongside our Water Arm. The choice is yours! [ Check this link for more about the Garden Watersaver
. Here's a great video by which shows you exactly how to install the Watersaver

Why is a combined intake/overflow better than a separate intake/overflow?

We've researched many rain barrel designs which have an intake and a separate overflow. A separated overflow is usually a hose of some sort coming out of the side of the barrel, near the top. There are some simple disadvantages to these systems: In some designs, the overflow is a standard 3/4 garden hose. A hose this small is simply not large enough to handle the Portland two-month winter deluge. Small-hose overflows, therefore, fail to overflow all the water coming in the top. This results in excess water gushing out of the intake (and everywhere else it can get through), inundating your foundation and flooding your basement. To remedy this, some overflow systems have a large (like 2-inch diameter) hose coming out of the top-side of the barrel. This handles deluges just fine, but there are three disadvantages: over 2 inches of fill capacity of the barrel is wasted (which translates to nearly 2 gallons lost); large-size hardware is expensive; the integrity of the barrel is severely compromised, so leaks are hard to prevent.

Furthermore, we've found that separate intake/overflow systems are much trickier for customers to install. A much more elegant solution is some sort of combined intake/overflow. In these systems, water comes in to the barrel. Extra water is diverted back to the system and then out (either to the sewer or to an on-site rain garden.) Products like the Garden Watersaver fill this need nicely and are easy to install with no specialized knowledge or skill. At Contain Rain, we offer the Garden Watersaver as well as our in-house diverter called the Water Arm.

Technical Principals of Liquids & Misc. Collection and Extraction Methods

PRINCIPAL: What is "Displacement"; and how does it work?

Archimedes discovered that any floating object displaces its own weight of fluid. Something placed within something must "displace" the molecules equal to itself. How else would it fit? The same principal applies to water flowing into a closed system occupied by air (it's not a vacuum). Where water goes in, an equal amount of air must go out. This is why most rain barrel systems must have a way of venting their air. Some methods of collecting rainwater have the air and water exchange in the same tube. When enough water enters, it creates pressure. This internal pressure forces air out (essentially 'clogging' the intake tube temporarily to let out air). The greater physical weight of the water 'falling' is enough to force its way past the air coming back out. Otherwise, the barrel would not fill. It's the same principal when you see air bubbles enter a water cooler as you are filling your cup, but in this example air is displacing water.

PRINCIPAL: So who is this guy Pascal, and why does water seek its own level; what does that even mean?

Blaise Pascal (b. 1623) was a French mathematician "of the first order". He built mechanical calculators and introduced new areas of mathematics research. His main contributions, as far as we're concerned, is his work in hydrodynamics and hydrostatics (centered on the principles of hydraulic fluids). In fact he invented the hydraulic press and the syringe. Fantastic! In the physical sciences, Pascal's law (the principle of transmission of fluid-pressure) states that "pressure exerted anywhere in a confined incompressible fluid is transmitted equally in all directions throughout the fluid such that the pressure ratio (initial difference) remains the same." (Bloomfield, Louis (2006). How Things Work: The Physics of Everyday Life (Third Edition).) Basically, he discovered two things that explain water seeking its own level, the first was that pressure on a liquid is transferred through the liquid equally in all directions (regardless of the amount of liquid present). The second was that pressure experienced by a liquid changed at different heights (barometric, atmospheric, or air-pressure), meaning that liquid which was physically higher in space had a different amount of pressure applied to it. Because of this principal, atmospheric pressure upon liquid in a confined and connected system will seek to equalize its level. And the weirdest part is that the physical amount or proportions of liquid in the equalizing containers doesn't matter. It will ALWAYS level out to exactly the same height from the ground.

PRINCIPAL: What about gravitational pull (the water's weight); won't that be sufficient to create water pressure?

Many people have this question and hold an intuitive belief that gravity will create a significant amount of water pressure (weight) at the bottom of the barrel and in turn force the water out a spigot and hose with considerable force. We admit, it would be fantastic if this were the case. However, for as heavy as water is, the only force with consequence is the force of air (barometric pressure) pushing down on the water. The water will essentially 'fall' out of the barrel, but with only the force of falling water. It will flow so long as it is falling (flowing downward). It will not fall with any pressure behind it, and if you are holding a hose higher than the top-most level of the water, it will not flow at all. Otherwise it will spill out with hardly any force whatever. This is sometimes desirable for those who wish to drip-irrigate with their rainwater.

PRINCIPAL: What is "wicking"? How can water move upwards against gravity?

Wicking is scientifically explained using a physics principal called capillary action. "Capillary action occurs because of inter-molecular attractive forces between the liquid and solid surrounding surfaces. If the diameter of [a] tube is sufficiently small, then the combination of surface tension (which is caused by cohesion within the liquid) and forces of adhesion between the liquid and container act to lift the liquid." ( Basically, we've all seen a meniscus in our drinking glass. Water has a magical property of "crawing" up surfaces that are unlike itself. Wicking is (more or less) a plethora of crawling meniscus, but each moment the meniscus encounters another particle to crawl up, hence the water soaks into certain material, even vertically. Water can wick almost 12" up through soil. For more information and a guide on soil wicking see The Permaculture Research Institute's page

ALT. METHOD: I want an extraction method that has good water pressure. What about pressurizing the barrels?

We have had a few folks who bought barrels from us with the intention of pressurizing them. To us, it doesn't make sense to pressurize the system at its most dangerous point; i.e. creating a potential explosion where all the water is stored. Most systems we have seen pick another point at which to introduce 'pressure'. It takes energy to create pressure, and a COMPLETELY sealed and sound system to maintain pressure (not even tires can always maintain their pressure). Why not use the energy on demand to create water pressure when you need it, like in a pump extraction method? Or if you must create and maintain pressure in the system, most we've seen use an air compressor attached to the system. In short, we do not recommend unnecessarily pressurizing the water barrels themselves.
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