Groundwater make up more than 95% of drinking water on Earth, but only 3% of it have a residence time of less than a century and a recharge rate high enough to allow its exploitation. Thus, assessing available groundwater volumes and their renewal rate (i.e., the age of water) are a strategic social issue, and also allows to estimate the vulnerability of water resources. Measuring the age of water is a major scientific challenge et requires developing reliable chronometers. In the next few years, Geotop will keep developing a wide range of tools (3H/3He, CFC, SF6) to measure short residence times (100 years and less) of water in order to identify available resources. It will also keep innovating with new, longer period chronometers (noble gases, >1000 years) to trace older groundwater resources, which are more and more exploited across the world.