Groundwater quality was monitored in four Spanish caves using concentrations of nitrate, potassium, phosphorus and in some cases total organic carbon. Three of the caves are located in NW Spain and contain prehistoric cave paintings and hence have special conservation interest. Of these, two are open show caves (Tito Bustillo and Pindal Caves), while the other one (Herrerías Cave) is not managed for tours and is partially closed off to public access. The fourth cave (Las Maravillas Cave) is located in SW Spain and is opened to the public because of its geological features and natural beauty. In this paper, we compare two sampling methodologies used in the four caves. In Pindal and Herrerias Cave high temporal resolution is achieved with a dripwater collector that collects discrete samples every 48 hours. In Tito Bustillo and Las Maravillas Caves a higher spatial resolution is achieved (16 sampling points in each one), but with a frequency of sampling ranging from 15 days to 6 months. Wastewater and livestock waste appear to be the principal sources of contamination to cave waters. Caves with concentrated livestock (stables) or urban and residential wastewater systems directly situated above the cave exhibit the highest level of contamination detected in elevated concentrations of nitrogen species and in some cases depressed oxygen availability in waters.