Time and space matter when monitoring faecal pollution : searching for efficient sampling designs in relation to hydrological regimes.

Luxembourg (2586 km2) is a rural country with rather small urban areas. Except for one main river basin, the contamination of surface waters and groundwater by faecal material is an episodic event. Therefore, classical monitoring schemes based on low, fixed sampling frequency turned out to inefficiently estimate the microbial water quality. Several studies have therefore been carried out on important drinking water resources (springs and surface reservoir) in order to understand the link between the faecal contamination events and the hydrology and the hydrology of these waterbodies. Physico-chemical and hydrological variables that could serve as relevant indicators for triggering selective sampling were also investigated.