Water and energy as inseparable twins for sustainable solutions.

Although the water cycle is only a minor contributor to the energy demand in society, it is a matter of good housekeeping to minimize the energy need within a sustainable water cycle. Wastewater treatment should not only be applied to purify the water, but also recover the energy present in this water, as well as to recover essential elements like nitrogen and phosphorus. From an energy analysis of the Dutch water cycle it is concluded that creating an energy neutral water cycle by using the heat content or by making use of the organic load of wastewater is within hands.