D2 Water Management Systems in Buildings

Topic

A building can significantly reduce its potable water consumption by reusing water from sinks and showers—which is relatively uncontaminated—for purposes that do not require potable-grade water, such as toilet flushing or irrigation; this creates a closed-loop system within the building for tasks that would otherwise consume potable water unnecessarily.

Additionally, rainwater falling on the roof can be captured and stored for these same non-potable uses; the usable volume depends on local precipitation, the available roof catchment area, and the fraction of rainfall that actually flows into the collection system rather than being lost to evaporation or absorption—a fraction that is very high with conventional impermeable roofing.

Both reused water and rainwater often require pumping to the point of use or to a storage tank, and this pumping entails an energy cost determined by the lift height, flow rate, and pump efficiency—the same type of cost described in the groundwater module regarding well extraction.

Thus, this module—which begins by addressing the reuse of water that would otherwise be discarded—concludes by demonstrating that managing a building's water involves more than just reducing potable water intake; it also entails utilizing two additional sources—previously used water and rainwater—available within or upon the building itself, even though both incur pumping costs similar to those of any other water in the system.

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