Pubdate: Thu, 13 Aug 2015
Source: SF Weekly (CA)
Column: Chem Tales
Copyright: 2015 Village Voice Media
Author: Chris Roberts

Nobody Knows How Much Water Cannabis Uses. That Hasn't Stopped Headlines.


This summer has been busy for law enforcement in California's Emerald 
Triangle, the sparsely populated rural counties where as much as 70 
percent of the cannabis smoked in America is grown.

Large raids in Humboldt, Mendocino, and Trinity counties have yielded 
few arrests - a cop convoy is not subtle and provided outlaw growers 
enough advance warning to flee, and at least one search warrant was 
served at a grow that was legal - but have turned up tens of 
thousands of plants, worth tens of millions of dollars, plus one 
startling find.

At a grow site in the remote Island Mountain area, sheriff's deputies 
discovered a football field-sized water bladder. Whether pulled from 
a now-dry creek or a spring, that's the kind of sight that fuels 
outrage in the fourth long, hot summer of California's historic drought.

The Island Mountain raid hit private land rather than the national 
forest, meaning it didn't hit the loathed trespass or "cartel grows." 
This was by design.

Raids are no longer staged based on mere plant counts. These days, an 
illegally-dug pond or poorly-built road is riskier for a marijuana 
grower than an extra row of plants. In a thematic shift, law 
enforcement is using environmental degradation as the reason for 
sending in the helicopters.

They're also using bad science.

The state Department of Fish and Wildlife is the lead agency on some 
of these raids. According to the DFW, a cannabis plant uses between 5 
and 10 gallons of water a day. That's a wide range, based on a 
back-of-the-envelope estimate which has become fact.

These numbers aren't derived from a scientific study but from a 
single source who now repudiates the figure. In 2010, the Humboldt 
Growers Association, a legal cannabis farmers' advocacy group, first 
published the 5-to-10 gallon figure during Humboldt County's brief 
(and abandoned) effort to regulate outdoor growing. This year, 
Emerald Growers Association, HGA's successor, has steadily 
backpedaled from the 5-to-10 gallon estimate. That's a "worst case 
scenario" that was never intended to represent an average, says 
Hezekiah Allen, the organization's co-founder and executive director.

The problem is that that figure has since been published in a string 
of scientific articles, including this month's issue of Bioscience.

"This isn't science. It was a guess," says Allen. "They're now taking 
that number and plastering it in the headlines, out of context."

And so far, the state's environmental scientists have stood firm.

"These are the numbers [DFW] uses and will continue to use," said 
Scott Bauer, a senior environmental scientist with the agency and one 
of the co-authors of the Bioscience article, in comments to the Sacramento Bee.

So how much water does a cannabis plant really use? The answer is 
that it depends. Which means the real answer, from a data-driven 
standpoint, is that nobody knows.

And now both the cannabis industry and the state's environmental 
stewards are pointing at each other and demanding a better-grounded 
figure. In the meantime, both the drought and enormous amounts of 
cannabis cultivation continue.

The cannabis trade is full of huge numbers. Medical marijuana sales 
top $1 billion in California. Legal cannabis sales exceed $2.7 
billion nationwide. Wholsesale, marijuana is a $16.7 billion cash 
crop, almost double the California's wine industry.

All of these numbers are estimates. You can thank cannabis 
prohibition for that. As with all wars, truth - or at least reliable 
data - was an early casualty of the drug war.

To date, there has been no comprehensive study of how much water a 
modern, commercially-grown cannabis plant uses.

How much water a cannabis plant uses depends not only on its size but 
also on how it's grown. Many of the plants seized during the Island 
Mountain raid were in one-gallon pots, Allen says. These, clearly, 
cannot use five gallons of water day. However, large plants that 
yield five pounds of cannabis or more at harvest could easily use ten 
gallons a day. (A better way to calculate water usage may be by 
yield; the industry says a pound of pot needs one gallon a day over 
an 150-day growing season.)

In an email to SF Weekly, Bauer says that a wide-ranging study is 
needed. Enterprising graduate students may take notice, but they may 
also be disappointed. Marijuana is an unregulated industry. Good luck 
getting grants from the government or enough growers to produce a 
peer-reviewed study.

"We all want better science on this," agrees Jeanette Howard, who 
heads the Nature Conservancy's water program and co-authored the 
Bioscience article. But for now, she says, "relying on the growers 
and what's been published in the past is the best we can do."

The industry points right back at the scientists. Agencies like DFW 
"have a mandate, and the mandate says to use science to protect the 
wildlife of the state," Allen says. "So give us a number, guys.'

What shouldn't be lost in all this is the premise of the Bioscience 
article: that cannabis production has an environmental toll. Nobody 
knows what the precise toll is, but that hasn't stopped people from 
guessing - or having those guesses accepted as gospel.
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MAP posted-by: Jay Bergstrom