The impact of current nitrate policy measures in Flanders is estimated. A modular modelling system has been developed for comparing response and pressure indicators and for decomposing the response impact of policy measures. Compared to 1990, the internalised manure surplus is reduced to zero, whereas the distance to target of the soil surface balance to the water quality standard dropped only with 58%. Source-linked and sink-related measures each account for about the half of the manure surplus reduction. The impact of abatement technologies is minor. The modular approach helps to unravel the discrepancy between pressure and response and to propose policy alternatives.