Triggered by the worldwide fresh water scarcity problem and the need for low cost water supply, Memstill is a newly developed membrane-based distillation concept, which has the potential to improve the economy and ecology of existing desalination technologies for seawater and brackish water to a large extent. This technology combines multi-stage flash and multieffect distillation modes into one membrane module. Because a Memstill module houses a continuum of evaporation stages in an almost ideal countercurrent flow process, a high recovery of evaporation heat is possible. The process promises to decrease desalination costs to well below 0.5 USD/m, using low grade waste steam or heat as driving force.