The presence of water in polymers, pharmaceutical substances or foodstuffs is often undesirable. A water content that is too high can reduce the shelf life of rice, make the processability of pharmaceutical products more difficult (for example tableting), or lead to quality problems with plastic products. The determination of the water content in different materials is therefore very important. Besides “water content”, the terms “moisture content” or “loss on drying” are also often used. In this article (Part 1), we will explain what the terms mean and discuss some of the techniques used to determine these quantities.