The lament of the Ancient Mariner, "Water, water, everywhere, but not a drop to drink," is echoed in many parts of the world but fortunately not yet in this country. However, looming water shortages in certain parts of the country, such as the Southwest and West, add urgency to the design of water conservation systems for buildings and developments. In addition many are becoming aware of the link between energy use and water use: in the West, considerable water use goes for the cooling needs of thermal (coal) electric power plants. In other words, as this area grows and electricity demand increases, water supplies come under double pressure. Nationwide, freshwater use for power production amounts to about 200 billion gallons per day.
Just as the building stock will be 75% new or renovated in 2035, compared with 2005, with all of the implications that has for energy use, by starting now, we can dramatically reduce overall water use for buildings, landscaping and neighborhoods by employing aggressive strategies to reduce consumption of potable water, following the mantra "Reduce, reuse, recycle." Water conservation in buildings involves reducing fixture demand, from conventional toilets using 1.6 gallons per flush (gpf) to low-flow toilets using 1.28 gpf (a 20% reduction), then to lower-flows at 1.12 gpf (a 30% reduction), perhaps even to 0.8 gpf (dual-flush toilets on the low setting).
We can eliminate the use of water for flushing urinals entirely, by using water-free urinals. We can reuse graywater (wastewater from sinks and showers, for example) for flushing toilets, and we can use onsite wastewater treatment in buildings to provide recycled water for such uses as toilet flushing and cooling tower makeup water. We can use both gray-water and municipally treated wastewater for landscape irrigation, as well as reducing water demand through xeriscaping strategies.
The key is to manage the entire water cycle, starting with what's free (rainfall) and trying to get as many uses out of that water as possible. For example, if you could reuse 80% of all water used in flushing toilets, you'd get the use of the same water five times. Then, even in a low-rainfall climate, you could have a major impact on water use. Becasue rainfall varies in the US from less than 8 to 12 inches per year in the desert regions to 36 inches in such places as Portland and Chicago, to nearly 50 inches in Orlando, it's important to look at each project's water resources as a starting point for developing design strategies.
The economics of water pricing in urban areas favors looking at the full system costs, including meter charges and connection fees. Reclaiming all the rainwater from a site, so that no storm-sewer connection is needed, can often result in savings that are greater than the cost of rainwater catchment and treatment. The same holds for onsite sewage treatment, particularly if the treated wastewater can be used for toilet flushing, cooling-tower makeup water and irrigation without ever leaving the project site. Why not take a more detailed and expansive look at the opportunities for 40%, or better, water conservation in your next project?
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