Finding the Payoff in Rainwater Harvesting
At the LEED Silver-certified Tacoma, WA, police vehicle maintenance facility, two 4,800-gallon culvert tanks collect rainwater and recycle it for toilet flushing. Courtesy of TCF Architecture, Tacoma.
Target Field, the new home of the Minnesota Twins, features an advanced rainwater harvesting and reuse system, the largest to date in professional
sports. Courtesy Wayne Kryduba.
The problem lies often in cost-benefit analysis of rainwater collection systems compared to most potable water prices, which are still quite cheap in the U.S. Using a ten-year cost analysis for a rainy U.S. climate, the rainwater collected over the ten years would cost approximately $4.55 per hundred cubic feet (CCF), which is higher than average water rates in most U.S. cities (but not necessarily higher than the highest-tier rates). The system wouldn’t quite pay for itself just with water savings because the added cost of extra plumbing to convey the water to the points of use hampers overall cost-effectiveness.
Although first-costs are higher than conventional systems, in new buildings rainwater collection systems could potentially eliminate expensive charges for storm-drain hookups, putting an owner “money ahead from Day One,” where the costs of savings are greater than the installation cost. In one project in which I was involved, just the cost of installing the storm drainage pipes to take water off the site and to connect to the town’s storm drains was greater than the cost of installing two 20,000-gallon tanks to hold runoff from the 100-year rainfall event and providing a treatment system that generates enough water for toilet flushing for a good part of the year. In addition, the use was for an academic building whose use pattern just about matched perfectly the annual rainfall cycle of the West Coast.
If seasonal and annual rainfall continues to be more erratic, water rationing and higher prices will be likely, making rainwater harvesting a rational economic response especially for large users. I harvest a few thousand gallons a year of rainwater at my house in southern Arizona, and I can tell you that nothing could be easier (or more sustainably satisfying) than using recycled rainwater for plant irrigation in a dry climate.