This chapter provides the context of water security for ecosystem-based approaches, notably nature-based solutions (NBS) operationalized in natural assurance schemes (NAS). The huge potential and value of nature-based solutions to both mitigate the effect of water while providing large and important co-benefits is addressed in this book and for this a deeper understanding is needed on how this contributes to water security and how barriers to implementation of NBS and NAS can be overcome. Firstly, relevant concepts and approaches of water security are introduced and reviewed; secondly, the assurance and insurance value is elaborated upon as distinct properties of ecosystem-based approaches; thirdly, the concepts of readiness levels for technology and knowledge, socio-institutionality and investment are introduced to address barriers for the operationalization of the value of ecosystem-based schemes to develop and harvest the full potential of climate resilient investments while addressing EU policies, including the Green Deal, Climate Adaptation Strategy and Strategy for Biodiversity. Finally, based on this chapter, overarching questions are posed which are addressed and discussed in the course of this book.