The aim of this study is to investigate the relationship between the use of plant protection products in agriculture and the impact on surface water quality. The spatial distribution of the agricultural use of plant protection products is estimated from detailed crop maps for Flanders, combined with results from a farmer survey on the use on different crops. Emission factors are calculated for different transport routes: drift, direct losses, volatilization, interception, erosion, drainage and leaching. From the maps of yearly use and the emission factors, emissions to surface water are calculated as the sum of drift, direct losses, erosion and drainage. The calculated substance emission is compared to measured concentration in surface water for a number of selected upstream areas. The resulting calculated emission maps have a resolution of 50 m and are used as input in the Water Emission Inventory System (WEISS).