Water demand for cannabis farming in California threatens watershed health, but to what extent? Without knowing how much water is being used where and when, policies to regulate water use will likely be inefficient and ineffective. Using data obtained from both permitted and unpermitted farms, our water-use models estimated the water footprints of cannabis farms across watersheds Northern California.

Models showed that cannabis water use concentrates in a subset of watersheds. It is not evenly spread across the landscape. Water extraction volumes for unpermitted farms consistently outpaced permitted cannabis in the dry season, when streams are most vulnerable to impacts from water diversions. Our scenario models investigated how compliance with current prohibitions on surface water diversions across all farms (permitted and unpermitted) would affect dry season extraction. We also modeled impacts of all farms modestly expanding off-stream storage. Then we modeled both strategies combined.

Our results suggest that water conservation efforts on California’s cannabis farms should focus on watersheds with greatest water demands. Programs that support expansion of off-stream storage can help reduce pressures on the environment and facilitate the transition of unpermitted farms to the regulated market.