Body water is tightly regulated to ensure we have just enough, and varies by no more than 1% daily in normal, healthy people (around 250-500ml). When body water decreases (e.g. due to sweating) or blood sodium levels rise, thirst is stimulated and the kidneys conserve fluid. Most people respond by drinking slightly more but, in a small number of cases, excessive fluid consumption can cause overhydration. In this new issue the effects of overhydration are reviewed, and practical tips to prevent it are provided.