4. Scale issues

Even with a variety of strategies for reusing and recycling wastewater, certain applications are not feasible at all scales. Treatment objectives, intended use, available technologies, and local constraints play a decisive role in determining the possibilities for recycling.

On a small scale—such as at the individual –, household, or building – level—greywater recycling is more suitable. It is generally carried out in a decentralized manner, particularly for uses such as flushing toilets, watering plants, or recovering heat via heat pumps. At this same scale, rainwater harvesting is possible, particularly through the collection of roof runoff, although the recoverable volumes remain limited.

With regard to stormwater, its reuse can also be implemented on a larger scale— –, city, metropolitan area, or even region— –, particularly through...