The rise in legal cannabis cultivation in California has brought a once-clandestine industry out of the shadows. Legalization has begun to illuminate the industry’s impacts on ecosystems and water—a particularly fraught issue as the state confronts a new drought. We spoke with Van Butsic and Ted Grantham, co-directors of UC Berkeley’s Cannabis Research Center and adjunct fellows at the PPIC Water Policy Center, to better understand how cannabis cultivation affects the state’s water.

Van Butsic

What is the extent of cannabis cultivation in California?

Van Butsic: We’re approaching 8,000 legal cannabis farms in the state, including permitted indoor and outdoor growing facilities. But most farms statewide are not permitted. To give you a sense of scale, we estimate that Humboldt and Mendocino counties alone had around 15,000 illegal farms in 2018. Permitted farms tend to be much larger than unpermitted farms, so by area it’s probably not as extreme as the farm numbers alone indicate

Ted Grantham:  Many legacy farms that were in operation prior to state legalization are still present, especially in Mendocino, Humboldt, and Trinity counties—the so-called Emerald Triangle. Most of the state’s licensed growers are also in that area. But we’re also seeing a shift in where legal cannabis is grown—especially in the Central Coast and Southern California desert regions.

Ted Grantham

What do we know about water use for this crop?

TG: Our research hasn’t found cannabis to be particularly thirsty relative to other crops.

VB: Legal outdoor production uses about the same amount of water as a crop like tomatoes.

TG: And cannabis farms are considerably smaller than other crops—on average, about a quarter acre. So, cannabis has a very small footprint and accounts for just a fraction of the water used by California agriculture overall. We see more variability in cannabis water use than other crops, partly because cannabis has avoided the standardization of production methods that we find in large-scale agriculture.

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