In the third year of implementing the 2030 Agenda for Sustainable Development, the World Water Week 2018 focuses on the very basis of our existence: the ecosystems on which all life depends, and the critical role of water in their functions. We depend on healthy ecosystems as habitats for plant and animal life, and for services for human development and well-being. In our development efforts we invariably affect and change our environment, but we need to do so without compromising the sustainability of vital ecosystems. The UN focuses on “nature-based solutions” as the theme for the 2018 World Water Day and World Water Development Report. In Stockholm we align the present 2018 Thematic Scope with this, and we go further to explore the wider water, ecosystems and human development agenda.