Streams in Northern California’s sensitive watersheds face multiple threats, including water use by cannabis cultivation. To start addressing this threat, we ask: how do cannabis farms source their water? Our study analyzed data from the Cannabis Waste Discharge Regulatory Program. Over 900 cannabis cultivators enrolled in the program, administered by Californa’s North Coast Regional Water Quality Control Board. The analysis identified cannabis cultivators’ most common sources for water, monthly patterns for each water source, and differences between the program’s compliant versus non-compliant sites.

Groundwater wells ranked as the most common source of water (58% of sites). Well extraction rates peaked during the growing season in April through October. Surface water diversions (22% of sites) and spring diversions (16% of sites), however, were distributed much more evenly across the year. Compliant sites used wells twice as frequently as non-compliant sites, 68% versus 33% respectively. As more sites join the regulated cannabis industry, wells may become more commonplace. How might an increased reliance on wells affect Northern California streams? We discuss the multiple factors at play. Answers to these questions can inform policy as regulators seek to address threats to streams and support a sustainable cannabis industry.