In 1991, City of Hannover, Germany commissioned William McDonough and Michael Braungart to develop a set of sustainability principles to guide development associated with the EXPO 2000 World's Fair in Hannover. The resulting document, "The Hannover Principles - Design for Sustainability" includes guidelines pertaining to water, which are included below. While these guidelines were developed for the World's Fair, they remain useful on a much broader scale.

"Water. Water is the most basic element of life on the planet—it will be celebrated as a fundamental life-giving resource. Opportunities to create understanding and enjoyment of water will be encouraged throughout the design or buildings, infrastructure and landscapes. Elements which celebrate the profound value of this resource on both material and spiritual levels deserve serious consideration. Designs will recognize the communal, cultural, historical, spiritual and poetic possibilities of the use of water and its central role as a precondition for life.

• Water use must be carefully accounted for throughout the entire design process.
• Water sources must be protected from contamination and careful consideration given to efficiency techniques at every step.
• Potable water consumption should only be used for life-sustaining functions.
• Water from aquifers, rain water, surface run-off water, gray water, and any water use for sewage transport or processing systems should all be considered within a cyclical concept.
• Waste water must be returned to the earth in a beneficial manner. Organic treatment systems should be considered.
• No ground water contamination should result from any use of water resources related to the construction or operation of any of the project's facilities.
• Design shall consider rainwater and surface run-off water as a possible resource for the inhabitants and in building systems and groundwater systems.
• Design should minimize impermeable ground cover.
• Gray water can be treated and applied to practical or natural purposes suitable to its characteristics.
• Water use in any process-related activity shall be put back inot circulation, and toxic chemicals or heavy metals should be minimized. All discharges of process-related water shall meet drinking water standards.
• Water, if used for sewage treatment or transportation, shall be restored to drinking water standards prior to distribution or reuse."

Source: William McDonough Architects and Michael Braungart. 1992. The Hannover Principles: Design for Sustainability. New York: William McDonough Architects.