This lecture explores the transport of water and solutes in catchments, focusing on water residence times and the use of tracers to understand hydrologic processes. It covers the EU Water Framework Directive, water quality parameters, and the distribution of water age. The presentation delves into the timescales of the hydrologic cycle, the advection-dispersion equation, and the significance of stable isotopes of oxygen and hydrogen as tracers. Various examples and data illustrate the concepts discussed, emphasizing the complexity and variability of water transport in natural systems.