While planet boundaries are being crossed and ecosystems degraded, the Ecosystem Service (ES) conceptrepresents a potential decision-making tool for improved natural resources management. The main aimof this paper is to assess the impact of forest cover on water related ES in Wallonia (Belgium) in termsof quantity and timing. We developed an approach based on easily accessible data, monitored in severalcountries and using straightforward statistical methods. This led us to study ES at “real-life” catchmentsscale: 22 catchments – from 30 to 250 km2– with mixed land covers were studied. We approached thewater supply and flood protection services through 5 indicators extracted from 10 hydrological years(2005–2014) discharge data series. These were computed annually and seasonally (vegetation periodfrom March to September and “non-vegetation” period the rest of the year). The water supply wasassessed through the specific volume Vs, the baseflow index BFI and the specific discharge exceeded95% of the time Q95s whereas the flood protection service was approached through the specific dis-charge exceeded 5% of the time Q05s and the flashiness index FI. Our study gives two main insights. First,statistical analyses show that forest cover negatively impact water supply when studying annual and“non-vegetation” period flows in general (Vs) but positively when studying low flows (Q95s). Regardingflood protection a slightly negative impact of forest cover on high flows (Q05s) was highlighted in the“non-vegetation” period. Results also show a negative impact of forests annually and in the vegetationperiod on the flashy behaviour of the catchment thus a positive impact on the flood protection ES. The“year” effect is overall highly significant testifying the importance of climatic factors. Rainfall is oftensignificant and can be considered as a main driver of these ES. Secondly, analyzing the quality of themodels produced and the results overall we assume that other variables characterizing the catchmentssuch as topography or soil types do play a significant role in the delivery of these ES. This questions theuse of land cover proxies in assessing and mapping of hydrological ES at a complex landscape scale. Wethus recommend further research to keep improving land cover proxies if they are used. ; Peer reviewed