Good news for gardeners! Rain barrels are now legal in Colorado. In 2017 House Bill 16-1005 legislation went into effect in August 2016, which allows homeowners to capture rain into containers up to 110 gallons total at any given time. The containers, usually barrels, can be joined together with hoses or separate.
The rain may only be harvested from your primary house, not a garage, barn or shed, before it hits the ground. It can also be collected on multi-family buildings with four or fewer units. Homeowner associations will allow them, although HOAs can make rules about where they are located, the color and style. At your own house, you can use home-made versions or store-bought ones, paint them fun colors or have them blend in as you wish. To be in conformance with Colorado water law the container must have a sealable lid. This is in part to reduce mosquitoes from breeding in the open water. A spigot low on the rain barrel allows you to turn it on to put water in a watering can or attach a hose going to your garden. An overflow hose at least 8 inches long at the top of the barrel keeps the extra water from spilling over the top and a screen at the top where the downspout goes into the container keeps out twigs and debris.
Water harvested can only be used outside on the same property where it’s collected for irrigation and is not for drinking, dish washing, bathing or indoor uses. It’s best to use it within a week but water can sit up to a month and empty containers at least monthly. Rain water is soft water, low in salts, is unchlorinated and may contain small amounts of nitrogen which benefits your plants.
A first flush diverter is recommended so that the first water entering the container isn’t full of contaminants from the roof, pollen, metals, bird droppings, dirt and other impurities. This diverts the first few gallons to a separate container than your storage container and could be a tip bucket style which dumps out or a float ball that closes off a diverted pipe when the water reaches a certain level, or a filtration diverter on the downspout. In some parts of Colorado there could be airborne arsenic or mercury, so a filter is helpful to reduce this being put on your garden or lawn.
Water collected and used is the not the same as having Water Rights under Colorado Law in effect since the 1850’s. This is a first in time, first in rights system with senior and junior water rights along the path the water travels. There is also a previous water collection law, Senate Bill 09-080, which allows eligible single-family home residents to apply for a Rooftop Precipitation Collection System Permit to capture water and use it for ordinary use inside including drinking, but not for outside uses or for watering plants in a greenhouse. These permit holders may use both collection rules.
For more details please see Colorado State University Extension Fact Sheet number 6.707 http://extension.colostate.edu/topic-areas/natural-resources/rainwater-collection-colorado-6-707/