Water Use in Cannabis Farming

Water Use in Cannabis Farming

Several of our researchers are studying the environmental impacts of water use by cannabis farms (see Carah et al. 2015, Butsic and Brenner 2016, Butsic et al. 2018, Dilliset al. 2019, Dillis et al. 2020).  The notoriety cannabis has received as a threat to water resources stems from early case studies of illicit cultivation in watersheds home to threatened populations of salmon and other aquatic species. This reputation has shaped water use policy at the state and county level; however, these policies are evolving as regulators and policymakers gain new information and adapt to a new regulated cannabis industry. Our goal is to provide research on water use and impacts by cannabis farming to support policy that accomplishes both environmental protection and successful development of a regulated cannabis industry.

Our work thus far has attempted to reexamine several assumptions embedded in early discussions of impacts to water resources by cannabis farming. The original narrative of cannabis as a threat to water resources was largely based on methods that relied on scaling water demand estimates by individual cannabis plants. However, we have found that the water sources and storage capacity of cannabis farms alter when water is actually withdrawn from the environment, thus emphasizing that diversion timing should be given greater attention than plant demands in estimating stream impacts (Dillis et al. 2020). In an effort to protect streams, multiple state and county policies have recently prohibited any diversion from streams during the growing season, thus requiring significant water storage capacity for farms relying on streams for irrigation. Unfortunately, developing sufficient water storage infrastructure (typically in excess of 100,000 gallons) appears to be a challenge for cannabis farms, especially given the rugged and remote terrain in which many are situated. This is an active area of debate in trying to find a middle ground between adequate streamflow protection and feasible compliance targets for farms participating in the regulated cannabis industry.

An additional revelation from our work has been that the majority of permitted cannabis farms are using groundwater wells instead of surface water diversions (Dillis et al. 2019). This observation has reframed how the stream impacts of cannabis irrigation are considered. Cannabis farms using wells are not required to store water and often draw water on demand throughout the growing season. While the impacts to streams are potentially less immediate, the use of groundwater wells introduces substantial
uncertainty into the determination of the timing and extent of these impacts. For instance, wells situated near streams can capture subterranean flow that would otherwise feed streams, or in some cases, pull water directly from streams themselves. Additionally, well use by cannabis farms may contribute to long-term stream flow depletion, according to modeling efforts conducted in collaboration with our team members (Zipper et al. 2019). The current understanding of the interplay between well location, depth, and underlying geology on stream impacts is still in its infancy, given the complexity involved, but is an important area of future research.

As the regulated cannabis industry continues to develop, policymakers will need to be proactive in dealing with a potential uptick in well use in the regulated cannabis industry. For cannabis farms that do not have the logistical or financial capacity to develop storage or reduce crop size (i.e. irrigation demand), wells are likely an appealing option. We have found that with increasing cannabis farm size, storage capacity is more likely to be insufficient (Dillis et al. 2020) and that outside of Northern California, outdoor cannabis is nearly exclusively irrigated with wells, especially among larger farms. However, if well use becomes tightly regulated, there may be little or no alternative irrigation sources for many farmers. 

Therefore, more work is needed to understand the relative impacts of groundwater wells and surface diversions on stream flow, how these impacts vary spatially based on water availability and hydrogeology, and how cannabis farming practices may respond to existing policies. These findings could guide refinement of cannabis water policy that is regionally tailored to balance environmental protection and promote the transition of illicit farms to the regulated cannabis industry.