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Water Determination vs. Water Activity in the Testing of Pharmaceutical Products

Water Determination vs. Water Activity in the Testing of Pharmaceutical Products

Water determination and water activity are two different concepts used in the testing of pharmaceutical products to assess their moisture content and potential for microbial growth or chemical stability.  Water determination is concerned with understanding the moisture content of a product and its potential impact on stability and quality.  Water activity is concerned with assessing the likelihood of microbial growth and chemical reactions due to the availability of water.

Here’s a breakdown between the two:

  1. Water Determination: Water determination refers to the measurement of the actual moisture content or water content present in a pharmaceutical product. It involves determining the mass of water present in a sample as a percentage of the total mass of the sample. This is typically done through methods such as loss on drying (LOD), Karl Fischer titration, or gravimetric analysis. The goal of water determination is to understand how much water is physically present in a product, which is important for maintaining the product’s chemical stability and shelf life. Excess moisture can lead to chemical degradation, microbial growth, and other undesirable effects in pharmaceutical products.
  2. Water Activity (aw): Water activity, often denoted as “aw,” is a dimensionless number that represents the availability of water molecules in a product for chemical reactions and microbial growth. It is a measure of the free water in a product that is available to participate in biological, chemical, and physical interactions. Water activity ranges from 0 to 1, with pure water having an aw of 1. The aw value provides insight into the potential for microbial proliferation and chemical reactions that might compromise the quality and stability of pharmaceutical products. Lowering the water activity can help reduce the risk of microbial growth and maintain product stability.

In pharmaceutical testing, both water determination and water activity play important roles in evaluating the quality and stability of products. While water determination provides insight into the actual amount of water present, water activity helps predict the potential for microbial growth and chemical degradation. Controlling both moisture content and water activity is crucial for ensuring the safety and efficacy of pharmaceutical products over their intended shelf life.  NJ Labs is skilled in the determination of the latest water activity (aw) procedures as described by the USP.  For more information:

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