Rainwater harvesting and collection systems: Barrels and diverters

Rainwater is free, doesn’t contain chlorine, doesn’t strain freshwater supplies, and doesn’t violate municipal restrictions on water use. A downpour on a 500 square foot roof can fill a 50 gallon rain barrel in a few hours. The roof might be covered with dirt, such as bird droppings, so the collected water should not be used for drinking. Watering the garden and washing the car, are common uses.

We look at how to choose a rain barrel and matching rain diverter, rain barrel sizes, leaf filters, and first flush diverters.

Some of the information in this article is based on consumer reviews of rain barrels and rain diverters, on the Amazon.com website.

Introduction to Rainwater Harvesting Methods

Practical rain collection systems make use of the house roof to collect water. A small 10 by 10 foot roof has a collection area of 100 square feet, about 100 times larger than the mouth of a rain barrel.

Placing a rain barrel (or tank) under the gutter downspout, is a simple and effective method of catching the rain (the bottom of the downspout can be cut off with a hacksaw, and an angled or flexible concertina downspout extender used to direct the water into the barrel). Placing the barrel under a rain chain will also work.

For gutterless roofs, the rain barrel can be placed at the point where the most rainwater falls off the roof (roof edges aren’t perfectly level, and will slope down to a few natural collection points). Less water is collected, compared to a gutter system, but is often enough to be useful.

More sophisticated systems tap into the downspout, and pipe water directly into an inlet port in the barrel. They are neater, less noisy and there’s less water splash but they are more difficult to install. Details are in the Rain Diverter section below.

Water is drained out through a spigot or hose. Pressure is low unless the barrel is elevated or a pump is used. Watering cans or soaker hoses are the normal ways of using water from a rain barrel.

Rain Barrels for Catching Rainwater

Rain barrels cost from $100 to $200 dollars and range from 50 to 75 gallons. Brands include Algreen, Fiskars, Achla, Koolatron, Emsco Group, Smartware, Rain Wizard, Great American, Heaven and Earth, Bosmere and RTS Home Accents. Larger barrels aren’t practical as they are difficult to transport from the store. Collapsible or knock-down barrels are more portable and go up to 200 gallons. They can be folded and stored indoors in winter. However they are less sturdy and should be avoided if possible. For more capacity, rain barrels can be daisy chained together.

Most rain barrels are now made out of plastic. Plastic is cheap, light and durable. It can be made to look like wood, stone or terracotta. It’s also easy to drill, seal and modify.

Useful rain barrel features are:

A screen cover to filter out leaves and mosquitoes. A DIY screen can be made out of fine netting or nylon stockings, stretched over the mouth of the barrel, fastened with elastic cord like a drum skin.
A safety grill to prevent animals and children from falling into the barrel. A fixed (not removable) grill is safer, but makes it difficult to clean the barrel.
An overflow port to channel excess water safely away from the house foundation and basement. The overflow port can also be daisy-chained (cascaded) to a second rain barrel. If the overflow port can’t keep up with the volume of water from the downspout, a larger hole or a second hole can be drilled.
An inlet port to allow water to be neatly piped in from a diverter in the gutter downspout, instead of pouring in from the top.
A spigot to fill watering cans. Many are located a few inches above the bottom of the barrel. This avoids dirt that collects at the bottom and makes it easier to fill watering cans, but also makes it harder to drain out all the water. A threaded spigot allows a garden hose to be connected.
An attached hose. This is usually attached below the spigot, and can be used to drain the barrel.
A drain plug. This is provided in barrels that have a high spigot but no attached hose. It’s use to clean out the barrel.
An elevated base, stand or legs to raise the barrel a few inches. This increases water pressure, and makes it easier to fill watering cans. Some stands are sold separately. Cinder blocks can be used instead.

Many of the above features can be added later if not included with the barrel. Missing ports can be drilled and accessories (hose coupler, spigot) added. Some barrels are sold with the accessories not installed: for maximum flexibility, owners choose where to drill the holes, and then install the accessories themselves.

Closed barrels have a sealed top. They are used with an inline diverter in the downspout. Water flows from the diverter to the inlet port and exits only from the spigot (the barrel isn’t completely sealed, to allow air to enter and exit as the water level rises and falls). They are child-safe but difficult to clean. When full of water, back pressure pushes any additional water back to the diverter in the downspout, making use of the downspout for overflow. An overflow port can be drilled for daisy chaining to other barrels, but the last barrel in the daisy chain should not have an open overflow port.

Some barrels have a tight pop-on cover, like a food container. They can be used as either a closed or open barrel.

Flat-back barrels are round in the front but flat in the rear. They’re like half barrels, designed to be mounted flush against the wall. One thing to look out for is the location of the various ports. Some overflow ports are placed at the rear of the barrel, which is inconvenient.

How Downspout Rain Diverter Valves Work

A rain diverter directs rainwater from the downspout into the rain barrel. They cost around $30 to $50. Brands include Rainreserve, Rainsaver, Fiskars, Inchworm, Great American and Mystic Rainwater. The main types of diverters are:

Fixed. The downspout is modified to always flow into the top of the barrel. The main problem is that the barrel’s overflow port might not be able to keep up with heavy rain.
Y or manual control. The downspout has two outlets, making it look like an upside-down “Y.” A lever is pushed to select the output outlet. One outlet flows into the top of the barrel, the other flows as normal into a drain or on to the ground. This allows the first few minutes of rainwater to be diverted away from the barrel. After most of the dirt from the roof has been washed away, the lever is pushed to direct clean water into the top of the barrel (assuming that someone is home, and awake, to push the lever). When the barrel is full, the water can again be directed to the drain.
First flush. This drains off the first few gallons of dirty rainwater, before diverting clean rainwater to the barrel. It’s like an automatic version of a Y diverter, but without overflow control.
Inline. A few inches of the downspout are cut away and replaced with the diverter. A hose connects the diverter and the barrel’s inlet port.

An inline diverter works best with a closed barrel. Back pressure from a full barrel causes the excess water to overflow back into the downspout. This means no worries over the barrel’s overflow port being too small to handle heavy rain.

An open barrel can be used if the diverter is installed at the same level as the barrel’s inlet port. If the water level rises above the inlet, enough pressure is generated to overflow the water back to the downspout.

The main disadvantage of an inline diverter is that not all of the water is diverted into the barrel.

Standard US downspout sizes are 3 x 4 and 2 x 3 inches. The diverter needs to match the downspout size. Adapters are available to convert from one size to another. Some diverters have two outlet ports, to allow two barrels to be filled at the same time.

A leaf filter should be installed in at least one position to prevent blockage:

at the top of the downspout (in the gutter)
inline with the downspout, for easy cleaning
at the top of the barrel (mesh cover)

Some inline diverters have a built-in leaf filter. An access panel makes it easy to clean out debris.

The Best Rain Barrel and Rain Diverter

Appearances are important. Homeowners who are willing to customize their rain barrel, can choose the one that looks best, then drill ports and add accessories as required. A thick, rigid wall is best for installing spigots and ports. Higher quality barrels have walls as thick as half an inch. In general, the heavier the barrel, the thicker the walls. A thick wall also lets less sunlight through (sunlight promotes algae growth).

An inline rain diverter is suitable for areas with high rainfall. In dryer areas that need to collect as much water as possible, one of the simpler diverters that divert 100 percent of the water, is a better choice.

It’s possible to combine diverters. For example, a first flush diverter can be installed on top of an inline diverter. This provides automatic clean water switching, and overflow back to the downspout.