Monitoring Water Activity Levels in Cannabis – What You Need to Know

by | Sep 29, 2022

Written by Kristina Etter

Kristina is a digital content creator and designer. She has a talent for creating engaging and informative content that resonates with our professional audience. Kristina’s passion for the cannabis industry stems from her belief that it has the potential to revolutionize the world in many ways, and has a personal testimony of cannabis success.

1. What is water activity in cannabis?

Water activity is a measurement of how much water is present in cannabis plant matter. While similar, water activity is a different measurement than moisture analysis, and it’s also different from water content.

We’ll spare you the scientific explanation of water activity and suffice by saying it’s an index for measuring the moisture condition of a product. Most foods have a water activity above 0.95 and that will provide sufficient moisture to support the growth of bacteria, yeasts, and mold.

Cannabis cultivators generally consider water activity to be a better analytic to determine the potential microbial content of a cannabis plant than moisture content. Testing for water activity early and often is certainly a more effective way to prevent mold than simply testing for common mycotoxin strains before a finished cannabis product is approved for sale.

2. What is water activity testing?

Water activity testing is when you test the water activity of a sample substance. Most cannabis analytics laboratories are equipped to perform water activity testing, and the GemmaCert Pro now makes it easy for anyone, anywhere to determine the water activity of a cannabis sample.

Most water activity tests work by placing a sample in a sealed container. Then, the vapor pressure of the sample and the surrounding atmosphere reaches equilibrium, and the testing device reads the humidity of the air in the sealed container to determine the water activity of the sample.

3. Why is water activity analysis in cannabis important?

Mold and other microorganisms can only thrive in cannabis in wet conditions. Generally, water activity in cannabis higher than 0.65 can lead to microorganism growth. By testing the water content of your cannabis at multiple stages in the drying, curing, and packaging process, you can ensure conditions in your buds never get wet enough to encourage microorganism growth.

4. Moisture analysis vs. water activity: Which is better?

Both moisture analysis and water activity are measurements of how much water is in a substance. Moisture analysis is a simple act of measuring the percentage of a substance water makes up. Water activity, on the other hand, is a much more subtle measurement that tells you how the water in a substance will interact with other substances—such as microorganisms.

From the perspective of preventing microorganism growth, therefore, water activity is the superior measurement. Moisture analysis will get you halfway there, but it doesn’t tell you anything about how the water content in a substance will interact with its environment.

5. What is the difference between water activity and water content?

Water activity is the measurement of how the water in a substance interacts with its environment, and water content is a much simpler measurement of how much of a substance water makes up. In the context of cannabis cultivation, water activity is a more useful measurement since it serves as a more accurate predictor of microbial presence than measuring the mere water content of your buds.

6. Can water testing analysis in cannabis identify microbial contamination?

Yes, water analysis testing is one of the best methods at a grower’s disposal to identify the presence of microbial contamination before it becomes a threat to yield. More accurate and informative than either moisture analysis or measuring water content, water analysis gives a grower a dynamic snapshot of how the water in their cannabis is interacting with its environment in the here and now, allowing you to take the action you need to take to protect your grow.

7. What is the range of water activity in cannabis?

Depending on its age and how it was handled, cannabis can land in many places on the water activity spectrum. Cannabis is only safe to store and transport, however, when it has a water activity level between 0.55 and 0.65.

If the water activity of cannabis is above this range, it will become highly susceptible to microbial contamination. Water activity in cannabis below this threshold, however, will result in dry buds with brittle trichomes2 that are easily destroyed.

8. What moisture level should cannabis be?

Water activity aside, it’s a well-known fact that the moisture content of dried and ready-to-smoke cannabis flower should be around 10-12%3. Moisture level is another analytic any responsible grower should keep track of, but when it comes to preventing microbial contamination, water activity is still much more important to monitor than the percentage of moisture in your buds.

9. What is considered a high water activity level in cannabis?

Water activity in cannabis is considered to be in the high range whenever it measures above 0.60. Cannabis remains in acceptable water activity parameters up until readings of 0.65, however, at which point the water activity in cannabis is considered to be too high. Steps should then be taken to prevent water activity above this threshold or else microorganism contamination may take place.

10. What is the low end of the water activity range in cannabis?

Dried and cured cannabis products that read below 0.55 in terms of water activity are in danger of drying too quickly or experiencing terpene degradation. Readings at or near 0.55 are acceptable, but if the water activity of your cannabis comes in at 0.50 or lower, you should take steps to rehydrate your cannabis to compensate.

11. How is testing for water activity in cannabis conducted?

You can test the water activity in a cannabis sample using a variety of different types of equipment. These days, it isn’t necessary to invest in bulky industrial equipment just to find out the water activity levels in your weed. Small, portable testing devices like the GemmaCert Pro provide fast, accurate water activity measurements without needing to take samples to the lab or bring all the lab’s equipment to your facility.

12. How do you calculate water activity?

If we want to get technical, the actual equation for determining water activity is equilibrium relative humidity divided by 100 or aw = ERH/100. You don’t need to know all of this, though, since cannabis testing devices with water activity functionality perform all these calculations automatically. Generally, only regulatory agencies like the FDA4 keep track of how to measure water activity manually anymore.

13. How do you perform in-house water activity cannabis testing?

With modern cannabis testing devices, performing in-house water activity testing for your cannabis products is easy. Simply connect the testing device to its mobile or desktop app, and select water activity as the measurement you’d like to obtain. Recent technology has made water activity testing much more accurate and compact, and the learning curve to become an expert at this form of cannabis testing has also lowered significantly.

14. Does a hemp water activity lab test work the same as a test for THC weed?

Yes, you measure water activity in hemp samples in exactly the same way as you measure water activity in high-THC weed. The dominant cannabinoid in a cannabis sample has no impact on the method used to test its water activity—simply place the sample in the testing chamber, and select water activity as the measurement you’d like to obtain.

15. How do you read a cannabis water activity lab test report?

With modern cannabis testing technology, determining the water activity results for a cannabis sample you tested is generally relatively straightforward. Portable cannabis testing devices like the GemmaCert Pro, for instance, provide a clearly segmented section for water activity in their test results—as long as you select water activity as a parameter you want to test ahead of time.

Remember that water activity will be represented as a decimal, not a percentage. Once again, the water activity window you’re going for in cannabis is 0.55-0.65.

Accurately analyzing cannabis water activity in-house is essential

The debate regarding how to properly test cannabis5 rages on across the country. While recognizing the necessity of testing for the presence of specific harmful microbes, regulatory agencies are also starting to respect the ability of water analysis to prevent microbial infection in the first place.

As a cannabis producer, the last thing you want is to get your products all ready for production only to learn they’re contaminated when you send them to the lab. By testing for water activity in house, not only can you avoid nasty surprises, but you’ll also have a much better shot of keeping your buds completely clean until they’re ready for sale.


1. Carter, B. P. (2020, November 11). The What, How, and Why of Water Activity in Cannabis. Cannabis Science Tech.

2. Livingston, S. J., Quilichini, T. D., Booth, J. K., Wong, D. C. J., Rensing, K. H., Laflamme‐Yonkman, J., Castellarin, S. D., Bohlmann, J., Page, J. E., & Samuels, A. L. (2019). Cannabis glandular trichomes alter morphology and metabolite content during flower maturation. The Plant Journal, 101(1), 37–56.

3. Leafly. (2021, February 26). What is moisture content? | Cannabis Glossary.

4. Office of Regulatory Affairs. (2014, August 27). Water Activity (aw) in Foods. U.S. Food and Drug Administration.

5. Seltenrich, N. (2019). Cannabis Contaminants: Regulating Solvents, Microbes, and Metals in Legal Weed. Environmental Health Perspectives, 127(8), 082001.