Cannabis Has a Water Activity Standard. Why Aren’t States Using It?
Cannabis flower sold in regulated markets across the country is routinely being dried below an existing national standard, according to a new analysis of nearly 145,000 laboratory samples.
The report, produced by the American Trade Association for Cannabis and Hemp (ATACH) with FTI Consulting, analyzed samples from 10 states. Average water activity fell below the range established by ASTM International’s D8197 standard in every state studied. In nine of the 10 states, at least 75% of samples tested at or below the bottom of that range.
ASTM D8197 calls for dry cannabis flower to maintain water activity between 0.55 and 0.65, a specification intended to protect both product quality and microbial safety.
The standard is not new. ASTM first published D8197 in 2018, and the specification was later incorporated into the National Institute of Standards and Technology’s Handbook 130, which establishes uniform laws and regulations for weights and measures. The cannabis provision was added in 2023.
Yet adoption of the standard by state cannabis regulators has been inconsistent, according to ATACH.
“Water activity sounds technical, but the stakes aren’t,” said Chris Lindsey, vice president of policy and state advocacy at ATACH. “Without a consistent standard, consumers get a worse product, patients face avoidable risks, and states leave real money on the table.”
Water Activity Is Not the Same as Moisture Content
Although the issue is often described in terms of moisture, water activity and moisture content are not the same measurement.
Moisture content measures how much water is present in a product. Water activity measures the water that is available to support chemical reactions and microbial growth.
ASTM’s standard sets both an upper and lower limit. Flower with water activity above 0.65 can create conditions favorable to mold and other microbial growth. Below 0.55, flower becomes more susceptible to physical damage and breakage during handling and storage.
Maintaining water activity within the range is also intended to preserve the characteristics of the flower during storage and distribution. Excessive drying can contribute to terpene loss and produce flower that is brittle and harsher to inhale.
Cannabis Industry Journal has previously examined the development of ASTM cannabis standards, including D8197 and its companion standard, D8196, which establishes procedures for measuring water activity in cannabis flower.
ASTM says water activity can be tested throughout the supply chain, from the completion of drying through merchandising.
Why Is So Much Cannabis Below the Standard?
The findings raise another question: Why is so much regulated cannabis being dried below 0.55 in the first place?
Cannabis cultivators have to control moisture carefully enough to prevent microbial growth while also meeting state testing requirements. Drying flower further can reduce the risk of mold or yeast developing before a product reaches the consumer, but the ATACH data suggest flower is routinely ending up below the range established by ASTM.
The report’s state-by-state analysis found the problem was not limited to one market or regulatory system. Average samples were below the ASTM range in all 10 states examined.
The findings also come as microbial contamination continues to trigger cannabis recalls. California’s Department of Cannabis Control recall database includes numerous flower and pre-roll recalls involving Aspergillus species. ATACH reported that 67% of California’s mandatory cannabis recalls between September 2024 and December 2025 cited Aspergillus.
Colorado presents a similar concern. According to the report, 61% of the state’s cannabis health and safety advisories between 2019 and 2025 involved mold or yeast.
Water activity control does not eliminate microbial contamination that is already present. ASTM D8196 describes water activity as a quality-control measure intended to prevent microbial growth and proliferation, not a kill step.
Overdrying Also Reduces Sellable Weight
There is an economic cost to drying flower below the standard as well.
Cannabis flower is sold by weight, and removing additional water reduces the amount of finished flower available for sale.
FTI calculated that a pound of cannabis flower dried from 0.65 to 0.45 water activity loses approximately 18 grams. Applied across commercial production, those grams add up.
FTI modeled the potential impact in five states and estimated that maintaining flower within the ASTM range could generate an additional $24.4 million in annual producer revenue in Arizona, $27 million in Colorado, $34.1 million in Massachusetts, $27.8 million in Missouri and $18 million in Nevada.
The analysis estimated corresponding annual tax revenue of $5.3 million in Arizona, $5 million in Colorado, $5.6 million in Massachusetts, $4.8 million in Missouri and $4.1 million in Nevada.
Those figures are modeled estimates, not documented losses. But they illustrate how drying practices can affect both cultivator revenue and state tax collections when flower is sold by weight.
A Standard Already Recognized by NIST
ASTM’s Committee D37 on Cannabis developed D8197 through the organization’s consensus standards process. ASTM currently maintains a growing collection of cannabis and hemp standards, covering areas including cultivation, laboratory testing, processing, packaging, and quality management.
The water activity specification eventually made its way into NIST Handbook 130.
The current handbook states that when unprocessed cannabis is offered for sale or ownership is transferred, water activity should be 0.60, plus or minus 0.05, in accordance with ASTM D8197. It also directs users to ASTM D8196 for the procedure used to determine water activity.
That puts the accepted range at the same 0.55 to 0.65 established by ASTM.
NIST Handbook 130 is designed to promote uniformity in weights-and-measures laws and regulations among states. Cannabis regulation, however, largely sits outside the traditional weights-and-measures system.
According to ATACH, state weights-and-measures agencies commonly incorporate NIST guidance, while cannabis regulatory agencies are not necessarily required to do the same. The result is that a nationally recognized specification for cannabis flower can exist without being uniformly incorporated into state cannabis regulations.
ATACH is calling on states to adopt the standard.
Doing so would raise several questions for regulators and cultivators, including when water activity should be measured, how long flower must remain within the specified range, and how compliance should be enforced as product moves from cultivation through packaging, distribution and retail.
ASTM D8197 covers more than the initial drying process. The organization says maintaining the specified water activity throughout the supply chain, from the completion of drying through merchandising, is important to preserving safety and quality.
For an industry that has spent years debating testing requirements and product safety state by state, the ATACH findings point to a different problem: a cannabis standard has already been developed and nationally recognized, but much of the flower being sold in regulated markets is still falling outside it.
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