Can Rainwater be Collected and put to Beneficial Use in Colorado?
The answer to that question is yes and no! What is helpful to answering this question is to split it up into “rainwater collection” and “stormwater detention.” A limited amount of rainwater collection is allowed at private residences for beneficial use; while stormwater that is required to be controlled in detention ponds and/or flood control structures has to be released without beneficial use.
Until recently the answer to the question would have been just “no;” however, that changed to a limited extent with the passage of Senate Bill 2009-80 and House Bill 2009-1129. The use of rainwater was subsequently expanded with the passage of House Bill 2016-1005.
Under Senate Bill 2009-80 rural residents with exempt wells may collect rainwater with a Rooftop Precipitation Collection System Permit from the Colorado Division of Water Resources. Under these permits there is not a specific limit to the volume of rainwater that can be collected and used; however, the rainwater may only be used for the outdoor uses allowed under the exempt well permit, which typically relate to the irrigation of not more than 1 acre of lawn and gardens and the watering of domestic animals (“domestic exempt well”).
House Bill 2009-1129 allows developers to prepare a concept for up to 10 pilot studies of rainwater harvesting projects and put it to beneficial, non-essential, use. These projects may only operate according to an engineered plan, submitted to the State Engineer for approval through a Substitute Water Supply Plan. Individual landowners are not eligible for these pilot projects. If the pilot plan is successful, the proponent has the option of taking the case to Water Court for adjudication of an augmentation plan.
Subsequent to the limited use of rainwater in rural areas, House Bill 2016-1005 expanded the beneficial use of rainwater by allowing single-family homes and multi-family units of four or less to collect rainwater in two rain barrels up to a maximum of 110 gallons for storage. While this is the maximum storage allowed, the rain barrels can be filled and refilled. Rainwater can only be collected from rooftop downspouts on your property and it can only be used for outdoor purposes, including irrigation of lawn, and watering of plants and gardens. Collected rainwater cannot be used for drinking or other indoor water uses. An important aspect related to this change in Colorado water law is there is no water right conferred by the capture and use of collected rainwater under either bill. Therefore, if the State Engineer was to conclude that rainwater collection and use is causing material injury to senior water rights, the ability to capture rainwater in some, or all, areas could be curtailed.
Stormwater detention is differentiated from rainwater collection, as stormwater detention relates to controlling runoff from large, low-frequency storms. This control may relate to flood control structures, detention of urban runoff, water quality detention facilities, or a combination of these stormwater management tools. Stormwater detention ponds are typically used to reduce peak flows from large stormwater flows in drainageways to protect property and lives, as well as to manage water quality. However, similar to rainwater collection, stormwater ponds do not have a water right. Therefore, stormwater needs to be managed but cannot be put to beneficial use. How do these competing interests get resolved within the Colorado Prior Appropriation system?
Mitigating peak flows to reduce and/or eliminate downstream damage to property and risk to human life is an important aspect of flood control structures and stormwater detention ponds. Large flows which would otherwise increase flooding are temporarily stored and released slowly to control peak river flows. In reducing peak flows and storing the water there is also time for water quality improvements. These improvements can be through the reduction in sediment loads as flow velocities drop, and through the use of vegetation to absorb some contaminants. To achieve protection against large peak storm flows and obtain some water quality benefits, stormwater can be stored for a set period of time, after which it has to be released without beneficial use so there is not injury to vested water rights.
Senate Bill 2015-212 codified the requirements for release of stormwater flows from a detention pond. Ninety-seven percent (97%) of flows from a 5-year storm or less has to be released within 72 hours, while for storms greater than a 5-year event, ninety-nine percent (99%) of the flows have to be released within 120 hours. Similar to rainwater collection, because no water right is conferred on a stormwater detention pond, if the State Engineer was to conclude that the detention of stormwater was causing material injury to senior water rights, the operation and/or design of the stormwater pond may need to be modified. It is possible to construct a stormwater retention pond, where the water is retained for eventual beneficial use. However, for stormwater retention ponds, a water right must be obtained prior to use.
LWS routinely works with surface water hydrology and water rights issues. For more information, please give Lytle Water Solutions a call or email us.
Phone: 303-350-4090
Bruce Lytle, P.E., bruce@lytlewater.com
Chris Fehn, P.E., P.G., chris@lytlewater.com
Ben Bader, ben@lytlewater.com
