The COASTAR 2019-2020 knowledge programme makes it clear: the subsurface can, as a supplement to surface options, offer an important source and storage space for a sustainable provision of freshwater. And this can be done by simultaneously tackling freshwater shortages, pluvial flooding and salinisation. Water users, water managers, drinking water producers, businesses, government and research institutes are pooling their strengths in the programme, so that sufficient freshwater will also be available in 20 years, at all times, for all users, and for all purposes. COASTAR represents another way of thinking and acting with regard to freshwater supply and water management, in line with the possibilities presented by the surrounding environment as well as the subsurface. The objective, following positive programme results and decision-making, is to launch four field trials in 2021. Founding partners of COASTAR are Allied Waters, Arcadis, Deltares and KWR.