A Reconsideration of Cannabis Water Use

Now that we are in a new period of extreme drought, the report of marijuana water use by Scott Bauer, Impacts of Surface Water Diversions for Marijuana Cultivation published in 2015, needs to be reconsidered and updated. The transition into an era of regulated cannabis cultivation needs to be based on rigorous, unbiased scientific data proceeding from realistic assumptions. The combination of insufficient data and the report’s admitted questionable assumptions makes the conclusions of the Bauer Report suspect.

Unfortunately, this report has shaped cannabis water policy since its publication. Many and various CEQA and EIR reports, as well as state and local legislation, make reference to the report’s conclusions. To counteract the impact of this report, at the risk of alienating the very agency whose approval I need, I offer a detailed critique of the report. To be frank, the report appears to me to be weak on science and strong on prejudicial assumptions. 

There can be no doubt that in order to better husband our water resources for the future, we all need to cooperate and share the responsibility for sensible, equable and scientifically based water allotments. I would suggest that given the astonishing recently re-discovered medicinal and public health benefits of cannabis, that cultivating this amazing herb is one of the most beneficial uses of the waters of Northern California. I would also state that the cannabis farmers who are coming forward to enter into compliance are, to the best of their ability and knowledge (in the midst of ever changing laws and regulations), attempting to cultivate this crop in an environmentally friendly manner.

The report, however, assumes the worst case scenarios based on visits to 40 cannabis grow sites in the company of law enforcement officers. Enforcement actions are by their very nature a response to extreme situations. They only see the bad actors and the most environmentally damaging cases. In statistical science this would be called a very biased sample population. To project those conditions from the worst grow sites onto the estimated 40,000 cannabis cultivators in the Emerald Triangle is unjust, unscientific  and discriminatory.

The report is based on many assumptions that display a prejudicial weighting of the evidence.

“Implicit in our calculations is the assumption that all water users are pumping water at the same rate throughout the day, as well as throughout the growing season.”

Assumption One-A: everyone is pumping at the same rate throughout the day. The truth is farmers water early in the morning or late in the day; some water every day and some every three days. Greenhouse and indoor grow water use is assumed to equal outdoor use. Ultimately, the report has to admit water use depends on many, many variables. 

“As with the cultivation of any crop, variation in average daily water use would be expected based upon many variables, including the elevation, slope, and aspect of the cultivation site; microclimate and weather; size, age, and variety of the plant; native soil type and the amount and type of soil amendments used and their drainage and water retention characteristics; whether plants are grown outdoors, in greenhouses, or directly in the ground or in containers and the size of the container; and finally, the irrigation system used and how efficiently the system is used and maintained.”

Realistically speaking then, there is no such thing as an “average daily” or total seasonal water use for any agricultural crop, since the microbiome and watering technique of every cultivation site is unique.

Assumption One-B: the same amount of water is taken each day during the 150 days.  In actuality, in the spring time only a few ounces are needed per plant per day. Normal watering does not commence until late June, when the starts are finally transplanted into the ground or larger pots. In September, water use is cut back as harvest approaches. Light Deprivation grows have smaller plants than outdoor grows and require less water. These crops finish harvest in early August and thus take no water after that. When they start the next grow right after that, the water demands for starts are minimal.

 Further, farmers by trade are very cognizant of water flows and water use. From experience, they know when the creek runs dry and when the plants need the most water. Out of necessity therefore, farmers capture water in storage tanks or ponds during the rainy winter months for use in the dry season. This practice is not taken in to account, as there is no mention of storage tanks or ponds in the report, which in fact dot the landscape where cannabis grows.

“Our calculations of water demand as a percentage of stream flow assume that all potential water users are diverting surface water or hydrologically-connected subsurface flow.”

Assumption Two: Every cultivator is taking water from the creek. The report makes no attempt to identify alternate water sources. There is no accounting for dry farming, rain catchment ponds or cisterns, contained springs or non-hydrologically connected wells. The contrived conclusion is that every cultivator is doing the same as the worst offenders.

The authors admit that there is very little reliable data available on actual cannabis water usage; they note that water gages’ accuracy “can be problematic” especially during low flow events; and they remark that they cannot confirm the contents of green houses. In light of these sources of inaccuracy, the data collected is hardly reliable.

In the analysis for Outlet Creek in Mendocino County, the data were collected from 1956 to 1994, so the most recent data in the report were at least 20 years old when the report was published. That means, there is no actual water use data for the year when the plant count for the report was estimated. In addition, if one looks closely at the lowest and zero flow years in the old charts, in each case the dates coincide with the drought years.

This bias became obvious early in the report, when a comparison is made between the water needs of one grape vine plant versus one cannabis plant. The implication is that wine is the good guy because pot uses twice as much water. But does it really? 

According to the California Department of Fish and Wildlife Report, a single grape vine uses 3.35 gallons (12.7 liters) of water per day or 503 gallons (1905 liters) during an entire season of 150 days. This one vine, according to a vintner friend, would produce a maximum of 4 to 6 bottles of wine. The retail value of five bottles of wine at $30 totals $150, from that one vine. 

The Wine Institute estimates about 2400 plants per acre in a typical vineyard. As per the annual Mendocino County Crop Report there are 16,500 acres of grapes planted in Mendocino County, which require 61,128 acre feet of water annually. (503 gallons X 2400 plants X 16,500 acres = 19,918,800,000 gallons of water per season which is 61,128.55 acre feet.)

On the other hand, again according to CDFW numbers, a single cannabis plant uses nearly twice what a vine uses or 6 gallons (22.7 liters) of water per day, totaling 900 gallons (3406 liters) per season. 

One cannabis plant produces, on average, one to two pounds of flower. However, growers often report four and five pound plants. A two pound plant would produce 256 eighths of an ounce, a standard retail unit, selling for $30 (like a bottle of wine), generating $7680 of income, compared to five bottles of wine from the one grape vine, retailing for $150.

In 2010, in front of a federal Grand Jury, the Sheriff of Mendocino County estimated there were over 5 million plants in the county, based on the 541,000 plants the department had eradicated the previous year.  How much water did all of these plants use? (900 gallons X 5,000,000 plants = 4,500,000,000 gallons per season which is 13,809 acre feet.)

How big an area would this cover? Even though plant size varies widely according to cultivar and cultivator, for an average assume each plant is 6 feet in diameter, so the canopy area is a bit less than 30 sq. ft. per plant. Thus the total acreage of cannabis plants in Mendocino in 2010 would have been 3,444 acres. (30 sq. ft. X 5,000,000 plants = 150,000,000 sq. ft. = 3,444 acres). This is just a tiny fraction of the 1,568,614 acres of the county which are not National Forest and at that time about one fifth of the total vineyard acreage.

These figures from 2010 can serve as a baseline for cannabis water consumption and acreage prior to legalization, when there were an estimated 10,000 cannabis farmers in Mendocino County. Now in 2021, with only about 1000 provisionally licensed cultivators in the county, both the acreage and water use must needs be significantly less, even assuming the many growers still operating in the “traditional market”.

To arrive at an accurate estimate of these two crops’ water consumption the comparison of wine grapes to cannabis flowers needs to be carried out to its logical conclusion. The 16,500 acres of grape vines planted in the County used 61,128 acre feet of water, which per the crop report created $100 million in revenue. The 3,444 acres planted in cannabis, on the other hand, used 13,809 acre feet of water and generated, according to popular belief, at least a billion dollars of revenue, probably more. 

To summarize, on one fifth the acreage, cannabis cultivation used about one fifth the water, yet produced at least 10 times the income. This is a low estimate. If there really were 5 million plants in 2010 and each one yielded one pound, the harvest would be 5 million pounds. At that time cannabis sold for at least $1000 per pound wholesale (more likely $2000 a pound). So the “real” total would be at least $5 billion in revenue coming in to the County. But that is a number from the past based on an estimate of 10,000 cannabis cultivators in Mendocino County.

Now in 2021, with 1000 legal growers and, who knows, maybe 5000 “traditional” growers still active, it is difficult to estimate the value of the total crop. About half of the legal growers have the maximum size permit 10,000 sq.ft., which could allow up to 300 plants. For averages sake, assume 500 growers x 200 plants equals 100,000 plants. Add to that an estimate of 50,000 plants for all the smaller size plots. So 150,000 plants producing two pounds each gives 300,000 pounds of premium flower. The current legal price is $1000/lbs. The sum total then is $300 million for the legal crop. Taxed at 2.5 percent of gross receipts this gives a hypothetical $7,500,000 to the County. (Actual receipts in 2018-2019 were $3.7 million and estimates of over $6 million for 2020. https://www.northbaybusinessjournal.com/article/article/cannabis-tax-revenue-doesnt-meet-sonoma-mendocino-projections/)

If one splits the illicit crop the same way, half doing 200 and half doing 100 plants the result is (2500 x 200 = 500,000 plants and 2500 x 100 = 250,000 plants) 750,000 plants and 1,500,000 pounds at $1000 per pound. This equals one and a half billion dollars on the illicit market. One would think that the County government would have an incentive to make it easy for everyone to come into the legal market to garner that tax money.

Moreover, the same cannabis plant that produces two pounds of cured flower, also produces at least a half pound of “smalls”. It will also produce at least a quarter pound of “trim shake”. The “leftover” smalls and shake can then be processed to make value-added medicinal products, such as concentrates, edibles, tinctures, salves, oils, etc. All that is additional product, created through value added processing, with very little additional water required.

So who is really using the most water in Mendocino? Wine grape cultivation in the county has expanded over the last several decades. From 1987 to 2015 there was a 5099 acre or 43% increase in vineyard area. Using the above formula, it required an additional 20,453 (33%) acre feet of water. This increase alone exceeds the total acres of cannabis cultivation estimated for 2010 and the increased water requirement was one and a half times the water used for the entire cannabis crop in 2010.

A more interesting number is the amount of water it takes to produce an eighth of cannabis. Most sun grown cannabis farmers grow plants that average between 2 and 4 pounds of manicured flowers. A two pound plant divided into eighths of an ounce yields 256 eighths.  Each eighth ounce then requires three and a half gallons of water (900gal. per plant per season divided by 256 eighths = 3.5 gal of water per eighth). An eighth ounce (which costs $30-$60) is a standard retail unit in cannabis dispensaries. A “standard joint” (one serving) uses about one gram, so an eighth yields three joints, meaning a joint takes a little more than one gallon of water. 

An eighth ounce jar of cannabis is a similar retail unit to one pound of beef, one bottle of wine, or one can of almonds at the supermarket.

It has been widely reported that to produce a pound of beef requires at least 1500 gallons of water, so a hamburger patty (one serving) uses 375 gallons. Wine uses between 200 to 400 gal per bottle, so each glass (one serving) needs at least fifty gallons. Almonds need one gallon per nut or about a hundred gallons per can, avocados about seventy-five gallons per pound, broccoli takes about five gallons per head. Cannabis uses a gallon per joint (one serving)!

Imagine then, a dinner party for four, with steak, wine, broccoli, avocado, almonds and cannabis. The total water consumption would be just over 1800 gallons, of which the cannabis share would be three and a half gallons of water.

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