What is Water Activity

Water activity, by definition, is the measurement of water vapour pressure generated by the free or non-chemically bound water in foods and other products. The bound water and moisture content cannot be measured directly with this method. The Aw value (range: 0.00...1.00 aw) is an important indicator for the shelf life of foods, pharmaceutical and cosmetic products and it strongly influences the occurrence and growth of micro-organisms.

Why measure water activity?

The free water in a product influences its microbiological, chemical and enzymatic stability. This is of great importance especially for perishable products such as foods, grains, seeds and particularly for pharmaceutical powders and tablets. If there is too much free water, the food is spoiled. Too little water can adversely affect product properties.


Read more in our Water Activity - Theory and Practise Section which includes presentations on ;

  • Introducing water activity 

  • Sample preparation guidance

  • Measurement best practise