Deryn Davidson, Colorado State University Extension – Boulder County

As the gardening season gets into full swing and you’re looking at your landscape with fresh eyes, it is a great time to reassess what worked last year, what didn’t, and perhaps start trying out some new ideas. Enter, rainwater harvesting! Rainwater harvesting is an age-old practice. Ancient civilizations developed the techniques to control flood water and collect rain for agriculture and domestic use. By shaping the earth, they were able to manage water and direct it to where they needed it to go.

There are two types of rainwater harvesting that you can employ for your landscape: ACTIVE and PASSIVE. Active rainwater harvesting is capturing water in a container for later use, or tank storage. Passive rainwater harvesting is diverting water overland to vegetated areas for immediate use, or soil storage.

It is important to understand that Colorado is a water rights state and this is key when considering active rainwater harvesting. Our water use is governed by the prior appropriation doctrine which, in layman’s terms, means a priority system – “first in time, first in right”. Essentially, when rainwater lands on the ground, it is owned by someone who hold water rights. Water in the arid west is no joking matter and the legalities around it are many. However, the good news for us is that through a study conducted by CSU it was determined that there would be no adverse effects on water rights holders and that rain barrels were a fraction of the total water balance.

In August 2016, House Bill 16-1005 was signed into law allowing Colorado residents to collect up to 110 gallons of rainwater, at any given time. With 110 gallons you can adequately water approximately 180 square feet with ~1” of water. It is important to note that your rain barrel will only be a supplement to your normal watering routine, but it’s something!

Active rainwater harvesting involves attaching a rain barrel to your gutter and downspout system. When it rains, the barrel will fill up quickly and you’ll be able to use that water later. The barrels must have a sealable lid and must be located above ground. You can purchase pre-made barrels or make one yourself. The most common DIY barrels are either 55-gallon trashcans with lids or old food grade barrels that you can get from bottling companies, bakeries, delis, and other bulk food service operations. DIY barrels must be properly retrofitted to conform to the state regulations. There are also regulations on what type of structure you can collect from and how you may use the water collected.

Passive rainwater harvesting does not fall within the issue of water rights because you are not holding the water for any length of time. It involves configuring your land to include elements that slow, spread and sink rainwater on your site. The goal is to keep it from rushing off your property and into the storm sewer. By creating berms (raised areas designed to slow), swales (raised areas designed to spread) and rain gardens (areas designed to sink) you are allowing the natural precipitation that we receive to infiltrate through your soil and plant roots and enter back into the ground water. Believe it or not, even when we get huge downpours, if you have a mostly flat or sloped yard, a lot of that water never makes it into the ground, but instead flows off your property, down sidewalks and driveways and into the sewers. Passive rainwater harvesting is not only good for your landscape, it also helps to clean water before it reenters the watershed.

If you are interested in how to incorporate active and passive rainwater harvesting into your landscape you can find more information about what is required at the CSU Stormwater Center, and on the CSU fact sheet “Rainwater Collection in Colorado – 6.707”.

Deryn Davidson is an Extension Agent – Horticulture at Colorado State University Extension Boulder County. For more information contact CSU Extension at the Boulder County Fairgrounds,
9595 Nelson Road, Box B, Longmont, 303.678.6386, e-mail [email protected] or visit