To protect freshwater habitat through California’s summer drought, state cannabis regulations restrict surface water diversions from April through October. To comply, farms that rely on surface water must either develop storage, reduce water demand, or seek alternative water sources, such as groundwater. Our study uses data reported by enrollees in California’s North Coast Regional Water Quality Control Board Cannabis Program to model impacts of cannabis cultivation practices on water extractions from the environment. We found that water input to storage in the off-season (November through March) reduced water extraction in the growing season (April through October). Despite this benefit, farms often lacked sufficient storage to eliminate surface water extraction during the growing season. The most important predictors of storage sufficiency were storage infrastructure, water source, and farm size. The likelihood of sufficiency decreased with larger cultivation areas. This self-reported data suggests that cannabis cultivation practices affect the need and timing of water extraction from California’s groundwater, rivers and streams.