Water systems today are designed to use water once and flush it downstream, with less than 0.3% of water consumed in the USA being reused locally. The growing constraints on water resources mean that we have to redesign our systems for significant reuse.
In our society, the image of reusing water is often unpleasant. This image is deepened by the conventional belief that all water must be treated to a drinking water level. Consequently, we use drinking water to water our lawns, flush our toilets, cool machinery, wash cars and equipment, and so on.
In fact, a number of studies have indicated that less than 20%-30% (depending on location) of water consumed needs to be potable (drinkable). Reusing water does not have to mean drinking recycled water.
The depth of the problem we face is documented in a 2010 study by the McKinsey Water Resources Group [ref. or hot link], which considered the global water picture over the next twenty years. They found a gap of 60% between all known conventional ways to increase supply and all known conventional ways to reduce demand. They identified a handful of unconventional strategies involving water reuse as the most cost-effective strategies to fill that 60% gap.
The conventional way of thinking about water, with our current centralized infrastructure also makes it very difficult to reuse water. Even in those cities that have installed municipal reuse systems, even the majority of those are centralized - requiring more energy and infrastructure to pump water back upstream to where the reuse demand exists. Decentralized, local systems would allow greatly expanded reuse that is less expensive, and has less of an impact on the environment, while being more efficient.
Today, have redesigned that infrastructure based on a natural ecosystem model. Natural ecosystems use and reuse water, and reuse it again and again locally for a wide variety of purposes. In the model provided by nature, a diversity of plants and animals – analogous to decentralized, municipal water consumers – use and recycle wastewater of varying quality from other consumers. Rainwater falling on a forest or grassland doesn’t just soak into the ground or flow into streams. The water is also shared by the plants and animals, each taking and passing along a rich store of nutrients for the use of other species.
This use and reuse of water can happen in a similar way throughout our communities. Water used in one way can be treated and reused and integrated into an interdependent local economy.