The environmental impacts of stream diversions are likely to be greatest during the dry summer months,which coincide with the peak of the growing season for cannabis. Further, because cannabis cultivation operations often exhibit spatial clustering , some areas with higher densities of cultivation sites may contain multiple, small diversions that collectively exert significant effects on streams . An important assumption underlying these concerns, however, is that cultivators rely primarily on surface water diversions for irrigation during the growing season. Assessments of water use impacts on the environment may be inaccurate if cultivators in fact use water from other sources. For instance, withdrawals from wells may affect surface flows immediately, after a lag or not at all, depending on the well’s location and its degree of hydrologic connectivity with surface water sources . Documenting the degree to which cannabis cultivators extract their water from above ground and below ground sources is therefore a high priority. In 2015, the North Coast Regional Water Quality Control Board , one of nine regional boards of the State Water Resources Control Board, developed a Cannabis Waste Discharge Regulatory Program to address cannabis cultivation’s impacts on water, including stream flow depletion and water quality degradation. A key feature of the cannabis program is an annual reporting system that requires enrollees to report the water source they use and the amount of water they use each month of the year. Enrollees are further required to document their compliance status with several standard conditions of operation established by the cannabis program. These include a Water Storage and Use Condition, which requires cultivators to develop off-stream storage facilities to minimize surface water diversions during low flow periods, among other water conservation measures. Reports that demonstrate noncompliance with the Water Storage and Use Standard Condition indicate that enrollees have not yet implemented operational changes necessary for achieving regulatory compliance. In this research, we analyzed data gathered from annual reports covering 2017 to gain a greater understanding of how water is extracted from the environment for cannabis cultivation. The data used in this study was collected from cannabis sites enrolled for regulatory coverage under the cannabis program.

The program was adopted in August 2015, with the majority of enrollees entering the program in late 2016 and early 2017. The data presented in this article was collected from annual reports submitted in 2018 ,flood and drain tray which reflected site conditions during the 2017 cultivation year. The data therefore represents, for the majority of enrollees in the cannabis program, the first full season of cultivation regulated by the water quality control board. Because the data was self-reported, we screened reports for quality and restricted the dataset to reports prepared by professional consultants. Most such reports were prepared by approved third-party programs that partnered with the board to provide efficient administration of, and verification of conformity with, the cannabis program. Additional criteria for excluding reports included claims of applying water from storage without any corresponding input to storage, substantial water input from rain during dry summer months and failure to list a proper water source. Reports containing outliers of monthly water extraction amounts were also identified and excluded due to the likelihood of erroneous reporting or the difficulty of estimating water use at very large operations. Extreme outliers were defined as those values outside 1.5 times the bounds of the interquartile range . Farms were not required to use water meters, and those without meters often estimated usage based on how frequently they filled and emptied small, temporary storage tanks otherwise used for gravity feed systems or nutrient mixing. The final dataset included 901 reports. Parcels of land where cannabis was cultivated — including multiple contiguous parcels under single ownership — constituted a site, and this is the scale on which reporting was conducted. The spatial extent of the cannabis program included all of California’s North Coast region ; however, only a subset of the counties in this region allow cannabis cultivation and therefore reports were only received from the following counties: Humboldt , Trinity , Mendocino and Sonoma . Because Sonoma County contributed relatively little data, we combined Sonoma County’s enrollments with those from Mendocino County when making county-level comparisons. The data used for this analysis included the source and amount of water that cultivators added to storage each month as well as the source and amount of water applied to plants each month. We did not analyze absolute water extraction rates. Rather, we used the amount of water extracted each month — whether water was added to storage or applied to plants directly from the source — to analyze seasonal variation in each water source’s share of total water extraction. Water sources included: surface , spring , rain , well , delivery and municipal.

The two external sources — delivery and municipal — were consolidated into a single category.Because staff from the water quality control board were not able to corroborate the accuracy of reported data, enrollees may have classified water sources erroneously. A well placed in proximity to a stream, for example, might properly qualify as a diversion of surface water; so might rainwater catchment ponds or spring diversions that are hydrologically connected to a watercourse. We attempted to minimize these potential errors by restricting the dataset to reports prepared by professional consultants. As mentioned, enrollees were required to assess several standard conditions in their site reports, including water storage and use requirements. To encourage cultivators to join the regulated industry, and because many cultivation sites existed prior to adoption of the cannabis program, existing sites were not required to comply with standard conditions as a prerequisite for enrollment. Rather, cultivators unable to comply with the standards when they enrolled were required to indicate their lack of compliance and develop a plan for achieving compliance. Such sites were not held in violation of regulations, thus removing a potential motivation to falsely report site conditions. More than one-quarter of enrollees in the dataset reported noncompliance with the Water Storage and Use Standard Condition. To address question 1 — from which sources cannabis cultivators most frequently extract water across the North Coast region, and if extraction patterns differ across the region — we calculated the percentage of sites that reported use of each water source . We also calculated, for sites using each source, the percentage of sites that also used at least one other source category. Directly applying water to plants and also placing water in storage did not constitute use of multiple extraction sources if the water was drawn from the same source category. Additionally, sites that used multiple inputs from the same category — for example, multiple wells — were not considered users of multiple sources, as this classification was reserved for extraction from multiple categories of sources. We performed all elements of our analysis for the entire dataset and for each county individually. To address question 2 — how reliance on each water source differed from one month to another — we divided each site’s monthly water extraction total by its annual extraction total to calculate the relative percentage of water extracted in each month, and performed similar calculations for each source category. The median amount of water extracted and interquartile range were calculated for each month — both for overall extractions and for each source category individually. To address question 3 — whether sites reporting compliance with the Water Storage and Use Standard Condition relied on different water sources than those reporting noncompliance — we compared water source extraction patterns for sites of both types. Specifically, we calculated for each compliance status the percentage of sites that extracted water from each source category and made comparisons accordingly; and did likewise for monthly extraction patterns, following procedures similar to those described in regard to question 2.

The purpose of this comparison was strictly qualitative, and no inferential statistics were performed to determine statistically significant differences. Instead, this element of our analysis was performed for exploratory purposes, with the intention of identifying broad trends that warrant future attention.The most commonly reported water source was wells . Over half the sites reported at least some reliance on wells for their irrigation water.Rainwater catchment and off-site water were the least commonly used water sources . Sites using wells and off-site sources were the least likely to use additional sources . In contrast, sites using rain catchment systems most frequently reported using an additional source category,hydroponic tables canada followed by sites reporting use of spring diversions and surface diversions . To determine if the observed high frequency of well use was due to bias associated with examining only reports prepared by consultants, we reincorporated sites without consultants and reran the analysis on this dataset . Reported well use was slightly more common among sites not using consultants than among sites using consultants . Counties displayed notable variation in the frequency with which cannabis cultivators used particular water sources . Compared to all sites in the dataset, sites in Humboldt County relied more on surface water and spring diversions , with fewer relying on wells . The pattern was reversed in Trinity County, with a high percentage of sites there reporting well use and relatively few using surface and spring diversions. A large number of sites in Trinity County were located in a single watershed known for a high concentration of similar cultivation practices, so we recalculated the percentages with these sites excluded. The resulting totals for Trinity County were closer to the overall results: wells , surface , spring , rain and off-site . Mendocino and Sonoma counties reported a similar pattern of extraction sources per site: wells , surface , spring , rain and off-site . Patterns of using multiple sources varied among counties. Sites in Humboldt County using well water extraction much more commonly used additional sources of water than did similar sites in Trinity and Mendocino/Sonoma counties. Use of additional sources was also more common among Humboldt County sites extracting surface water and spring water than among sites using surface and spring water in Trinity County and Mendocino/Sonoma counties . Wells were a prominent water source for cannabis cultivators during the summer months . Extraction from wells generally peaked in August and declined in off-season months. The pattern was reversed for rainwater use, with most extraction occurring in off-season months. Spring water use was generally even across the year, with slightly higher use during the growing season. Surface diversions occurred throughout the year, but declined late in the growing season, likely reflecting declining availability of surface water. The pattern exhibited in off-site water use closely matched that of well water; the former, however, was a less substantial source of water in general. There appeared to be differences in the extraction sources reported by compliant and non-compliant sites .

Although nearly one-third of non-compliant sites used well extraction, this source was more than twice as frequently reported among compliant sites . In contrast, non-compliant sites reported surface diversion and spring diversion more commonly than did compliant sites . Rain and off-site sources were the least commonly used for both compliant sites and non-compliant sites . Use of additional alternative sources was lower for compliant sites with wells than for non-compliant sites with wells . The seasonal extraction patterns of compliant and non-compliant sites were generally similar , following the overall pattern discussed above.We found that well water is the most commonly reported source of extracted water for cannabis cultivation in the North Coast region of California. Furthermore, among the source categories, wells are least frequently supplemented with alternative sources. Spring and surface water diversions together are also important water sources, with seasonal patterns of use that are distinct from well water extraction. Reported timing of well water extraction closely tracks the water demand patterns of plants, indicating that cultivators are applying well water directly to plants, rather than storing it. In contrast, the timing of extractions of spring water and surface water remains relatively consistent throughout the year, suggesting that water from these sources may be diverted to storage in the winter, reducing the need for extraction in the summer months. These seasonal extraction patterns and the relative predominance of each source may inform assessments of cannabis cultivation’s impacts on water availability.