The wastewater reuse and water-saving schemes described above are each tailored to a particular scale of implementation (from single homes to entire countries), population density (from urban to rural), and level of technological sophistication (from high-tech to low-tech) (Fig. 3A). Potable substitution schemes using advanced wastewater treatment may be feasible in an urban context, but not in a rural context. Furthermore, no single scheme simultaneously maximizes wastewater reuse, minimizes wastewater generation, and minimizes stormwater runoff (Fig. 3B). How does a community identify the right mix of schemes that will optimize their water systems? One study evaluated infrastructure options for a hypothetical residential development in the southeast of England, and concluded that every community has a technological
state-of-the-art equilibrium beyond which tradeoffs are required (41). Wastewater reuse and water-saving schemes can improve water use, energy use, and land use up to the equilibrium point.Beyond the equilibrium point, further reductions
in water use require increasing either energy use (if high-tech options are used) or land use (if low-tech options are used) (41). Human behavior should also be considered in the assessments of optimal water management strategies,