Due to climate change and increased demand, potable water (also known as drinking water) may be in short supply in the coming years. As global temperatures rise, changes in evapotranspiration and precipitation are supercharging both the high number and rapid intensification of droughts. To make up for the lack of rain, more ground and surface water will be needed for landscaping and agriculture. Already, the EPA estimates that landscape irrigation accounts for one-third of all residential water use, and makes up as much as 60 percent of water use in dry climate regions. This is where local governments come in: as the primary land use authority in the United States, cities, towns, villages, and counties can regulate the ways in which water is used and even sourced.
Rainwater Harvesting: What Is It?
Rainwater harvest is a water conservation strategy that involves directing rainwater to plants and landscapes as a form of “natural” irrigation. The goal is to take rain that would otherwise evaporate on impervious surfaces or be swept away down drainage systems and use it instead to water areas that need it.
There are two primary methods of harvesting: active and passive harvest. Active rainwater harvest occurs when rain falls onto a roof or other impervious surface and is then directed via gutters or drains to a holding space. The holding area stores the water until a later date, when rain may be infrequent or when the plants are ready to be watered again. Alternatively, passive rainwater harvest is a method of landscaping and structuring impervious surfaces so that water is directed right to the target flora whenever it rains.
Graphic by the author.
Graphic by the author.
Rainwater Harvesting at Work
The American Southwest is known for its dry, desert landscapes and hot temperatures. While communities in Arizona, New Mexico, Nevada, California, and Utah have faced droughts throughout history, many have become more resilient through the utilization of local land use law.
The City of Tucson, AZ, has implemented a rainwater harvest ordinance aimed at commercial developers to promote water conservation. The watershed that provides water to Tucson has been in a state of drought 85% of the time since 2000, and with a population of over half a million, the city is no stranger to water stress. In 2010, Tucson Unified Development Code Section 4-01.0.0 went into effect. This code requires that all commercial development plans include a rainwater harvesting strategy to meet 50% of landscape water needs. The ordinance gives flexibility to developers in deciding between passive or active rainwater harvesting systems and provides design considerations and requirements for both. Developers must submit a Rainwater Harvesting Plan, which includes a Water Budget and Water Harvesting Implementation Plan, as part of their commercial development application. This ordinance is enforced through inspections conducted by the Tucson Planning & Development Services Department (PDSD) and annual reports submitted by commercial site owners. As of January, 2022, 137 rainwater harvesting plans had been approved by the City.
Not all municipalities use the same rainwater harvest requirements. The Albuquerque Basin Aquifer, which supplies water to Bernalillo County in New Mexico, has a history of being depleted faster than it can recharge. As a result, , Bernalillo County requires that developers incorporate water conservation methods into construction plans. Under Bernalillo County Code Chapter 30 Article VII Section 30-249, commercial and large multifamily developers are required to choose four out of seven listed water conservation measures to include in their construction plans. Two of the optional measures are passive and active rainwater harvesting. The key distinction between Tucson and Bernalillo County is that Tucson’s code requires that developers include water harvesting plans in their commercial development application, whereas Bernalillo County offers water harvesting as two possible choices out of a list of water conservation measures. These two examples go to show that there are different ways to integrate rainwater harvest requirements into local land use codes, and the choice is dependent upon localities’ preferences and needs.
Enabling Conditions
Building up resilience to climate impacts does not happen overnight. Implementing codes to effect change requires a multitude of factors to be present and in alignment. The Intergovernmental Panel on Climate Change (IPCC) has identified such factors as enabling conditions, which help “enhance the feasibility of adaption and mitigation.” The IPCC’s Sixth Assessment Report identified six categories of enabling conditions, three of which are exemplified by Tucson and Bernalillo County: political commitment and follow-through; institutional frameworks, policies and instruments; and inclusive governance processes.
Enabling conditions are especially important in the context of rainwater harvest implementation. The City of Tucson incentivizes rainwater harvest by offering up to $2,000 in rebates to residents. The City also published a Water Harvesting Guidance Manual for developers, engineers, and contractors of commercial sites, public buildings, and subdivisions. Bernalillo County subsidizes the cost of rain barrels for active rainwater harvesting, hosts rainwater harvesting workshops, and provides contact information for water harvest experts on their county website in both English and Spanish.
Taken together, these efforts enable effective implementation of their respective rainwater harvest ordinances by raising public awareness, incentivizing behavior, and addressing relevant social inequities such as income disparity and language barriers.
Cuidad Soil & Water Conservation District (a political subdivision of the State of New Mexico) partnered with Bernalillo County to construct this prototype for a passive water harvest swale and basin. Together, they also produced instructional videos about how rainwater harvest systems can be constructed economically.
Jurisdictional Constraints
While harvesting rainwater is an easy way for local governments to promote water conservation, the feasibility of enacting water harvest ordinances depends on jurisdiction. Western states may covet water rights in ways that prohibit rainwater harvest. One such example is Colorado. Until recently, the Colorado state constitution declared that all rainwater belonged to Colorado’s water rights holders. The reasoning was that harvesting rainwater would infringe on the water rights of senior water rights holders who depended upon streams and groundwater systems partially supplied by rainwater. This prohibition on rainwater harvest ended in 2016 when Colorado passed Senate Bill 09-080. Now, residential buildings with fewer than four units may collect up to 110 gallons of water throughout the year.
The takeaway from Colorado is that local governments should, as with all other ordinance proposals, check with state law before enacting a local water harvest code. If there are codes a locality wishes to impose, but that would conflict with state laws, it may be worthwhile to collaborate with state legislatures to remedy such restrictions.
Rainwater harvesting is a great way to conserve potable water, especially in the face of increased drought severity due to climate change. Rainwater harvesting codes can help localities adapt and become resilient to rising temperatures. As demonstrated by the case studies discussed here – City of Tucson, Bernalillo County, Colorado – a wealth of information and resources is available to local governments interested in implementing similar codes and adapting to climate change.