Groundwater in the Motril-Salobreña coastal aquifer was studied using various tracers to determine its age and flow patterns. The researchers found that groundwater in the shallow areas is young, less than 5 years old, while deeper areas contain water up to 170 years old. Saltwater intrusion affects the mixing of ages in the aquifer. The flow is faster near the surface and slower at depth, with different residence times in different parts of the aquifer.