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Measuring water activity - measuring humidity - measuring and monitoring AW values

Water activity measurement – Moisture measurement – measuring and monitoring AW values

What is water activity (AW)?

Water activity ( AW) is a parameter that quantifies the availability of water in a food (it is a measure of the volatility of water molecules). AW is given as the ratio of the partial pressure of water vapour over the food at a given temperature to the partial pressure of water vapour over pure water at the same temperature. Water activity increases with temperature. The moisture status of a product can be measured as equilibrium relative humidity (ERH) expressed as a percentage, or as water activity expressed as a decimal.

If there is too much water in the product, there is a risk of microbes growing and carrying water to other corners. This can lead to lumping, changes in consistency and a reduction in the shelf life of the product. For example, food and pharmaceutical manufacturers must. FDA to show that the water activity of the product has decreased to the point where bacteria no longer need to grow in it.


As the measurement of water activity or ERH is a key parameter in the quality control of moisture-sensitive products or materials, our partner Rotronic offers a range of solutions for monitoring, monitoring and control of moisture and/or ERH in their product range, which can be viewed in brochure . From this programme, we highlight the following two AW measurement devices.

Laboratory device for measuring water activity – an innovative and autonomous user interface

From our product range, we would like to introduce the innovative HYGROLAB laboratory device for measuring water activity, with up to four sensor inputs. The device allows simultaneous or asynchronous AW speed measurement. Operated by a high quality touch screen. The AW meter can also be connected to the internet for remote control via PC or tablet. Measurements can be monitored (real-time) and measurement reports can be uploaded anytime, anywhere.

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Image: HygroLab laboratory device for measuring water activity


  • High accuracy ±0.008 AW at 23 °C
  • up to 4 measurements simultaneously or asynchronously
  • fast and easy operation (mouse and keyboard)
  • AW Quick function for fast measurement results (typically 4-5 minutes)
  • measurement of: temperature, water activity and relative humidity
  • independent setting of the set point for quick and easy display of results
  • remote monitoring with the possibility to download measurement reports
  • the possibility to download regular software updates with enhanced features directly from the HygroLab device
  • automatic report generation after each measurement
  • FDA regulatory compliance
  • the possibility to calibrate the sensors.

Portable water activity analyser

From our product range we offer HygroPalm portablewater analyser ideal for measuring AW in production or storage systems (e.g. inspections of cheese, meat, tobacco, building materials, animal feed, bakery products, paper medicines, etc.).

for measuring water activity
HP23-AW-A Portable Water Activity Analyser, HygroPalm


  • for measuring water activity, relative humidity and temperature
  • 2 input channels can be connected for HC2 probes or HC2 probe probes
  • FDA 21 CFR Part 11/GAMP5 compliance

Here you can watch a YOUTUBE video explaining the steps to measure water activity in 5 minutes (AW-Quick).

For use in

pharmaceuticals, tobacco, food and many others.

Author Katarina Žunko, source PST: ”Water activity”
November 2020

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