The Department 22 team ran a one-week interdisciplinary workshop to support Hitachi EU in its quest to explore the future opportunities of grey water. Participating groups were asked to create entrepreneurial ideas based on a randomly allocated city and a specific demographic, using persona building and story-telling to evolve viable ideas for the future. Brainstorming briefs investigated different possible themes, such as ‘Packaged Water’, ‘Water as a Currency’, and ‘Living Home’. Ideas included Water Walla, a water delivery service in the Bhalswa slum, Delhi; a new grey water product system in London; and a technological connected home in Tokyo. This latter idea, incorporating nano-technology and the use of algae for an energy- and water-independent home was developed further following the workshop.