Finishing Line - June 2008

Rain: Save It, Put it to Work
By Robert Roman

In arid countries, water scarcity threatens food security, human health, and natural ecosystems. As a result, many of these countries are embracing the concept of urban rainwater harvesting to make up for the depletion of ground water aquifers, lakes, and natural hydrological courses.

Rainwater harvesting is the process of collecting rainfall and storing it for later productive uses. Harvesting rainwater dates back to 4,000 BC when it was used for agricultural and water supply purposes. Given the drought conditions that exist today in many regions of the world, rain harvesting is becoming more popular. In Singapore, 45 percent of the land area is being used for water catchments. Bangalore has plans to use rain harvesting to supply up to 25 percent of the city’s total water requirement by 2010. In Chennai south India, rooftop water harvesting is now compulsory, and 98 percent of buildings are reported to be in compliance.

Despite its long history, rainwater harvesting is rarely practiced in the United States because we are accustomed to a safe and abundant supply of water that is made available by public and private utilities. However, the growing demand for potable water, aging infrastructure, rising cost of treating wastewater, and over-pumping is pressuring many utilities to raise water and sewer rates and/or curtail the use of fresh water during periods of drought.

The process of rainwater harvesting involves catching it, directing it to an appropriate location, filtering it, and storing it for later use. At a car wash site, rainwater harvesting could include capturing rainfall from rooftops and intercepting the surface water run-off that would normally flow to a storm sewer.

Harvesting rainfall from rooftops would involve installing or utilizing existing gutters and downspouts and piping the water to the harvesting collection area. The other components of the system include a strainer basket to remove foreign objects, washable water filter, above or underground storage facility, plumbing, float switch, and submersible pump.


A new self-service wash with four wand-bays, one in-bay automatic (no reclaim) plus allowances for employee use, wash-down, and maintenance will use about 1.26 million gallons of fresh water annually. Based on a rate of $3.00 per 1,000 gallons, the annual water and sewer cost for this wash would be $3,780.

The accounting cost of installing a rainwater harvesting system for this wash would be around $50,000. However, the economic cost would only be $40,000 because the spot-free quality of the rainwater would provide the opportunity to save the cost of a reverse osmosis system.

Based on annual mean rainfall of 35 inches, the harvesting system would produce about 580,000 gallons of usable water. This represents a 46 percent reduction in fresh water consumption and the investment would have a payback period of 22 years. However, if water and sewer rates were to triple, as they have for some car wash operators, the investment would have a respectable payback period of less than eight years.

If we added a reclaim system for the in-bay automatic, the economic cost in our example would increase to about $70,000. However, the combined effect of water harvesting and reclaim would result in a 63 percent reduction of fresh water and, if water and sewer rates were to triple, the investment would have a similar pay-back of less than eight years.


Besides saving fresh water, the benefits of combining rainwater harvesting and reclaim would include the eventual reduction in operating expenses, insulation from mandatory water restrictions, goodwill from marketing the wash as a “green” business, and quite possibly credits and/or subsidies to help defray the cost of the system, which would further reduce the pay-back period.

Rainwater harvesting may not make much sense for car wash operators who are located in areas like Utah where it does not rain very much. However, for operators who are facing significant water and sewer rate hikes, curtailment of fresh water use, and are located in areas with sufficient annual mean rainfall, the payback and return on investment of water harvesting and reclaim will continue to become more attractive.

Robert Roman is an analyst and lead consultant for RJR Enterprises, a consulting firm based in Clearwater, FL ( You can reach Bob via e-mail at

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