Harvesting Rainwater   Rain cisterns are an ancient solution to a still-pervasive problem. Widespread use would stretch urban water resources and temper the impact of storm-water run off.   In the summer of 1987, we sold our farm in the North Carolina Mountains, and I began looking for a location in Virginia's Shenandoah Valley to relocate a federally licensed goat cheese creamery. For someone who had spent his youth and college years in booming Atlanta, farm hunting in the beautiful Valley was like touring a foreign country. As John Denver wrote over four decades ago, “Life is old there, older than the trees.”   Intensive cultivation of 50-acre farms by 18th-century Germanic immigrants had left its imprint on the landscape. There were literally thousands of Colonial and Federal period houses in the Valley. The roadsides were dotted with historical markers describing massacres during the French & Indian War, or battles during the Civil War. The buildings and technology utilized in the old farmsteads were also very different from what I had known in the Deep South.   One of the most interesting technologies found on nearly all Shenandoah farms was the rain cistern. The northern Shenandoah Valley is one of the driest regions east of the Great Plains. Most of its 28 inches of precipitation occurs during the winter and spring months. Most shallow wells go dry by mid-summer. The settlers dealt with the dry months by building brick masonry cisterns underground and channeling the rainwater from their roofs into them. During the summer and fall, the cisterns functioned just like wells. Nowadays, if the cisterns go dry, the farmers purchase bulk water from bulk haulers, who pump their water from mountain springs.   Cisterns are still installed for new homes in the Valley that are outside the jurisdiction of public utilities.  Often the rainwater is filtered before entering the cistern. Periodically, homeowners add purification tablets to the prefabricated concrete water tanks to cut down on the growth of yeasts and bacteria. The cistern water is used for washing clothes and vehicles – also watering gardens – while sterilized  well water is utilized in bathrooms and the kitchen.   The concept of cisterns is an old one. The Mayas of the Northern Yucatan Peninsula constructed enormous cisterns as their villages became cities. The Northern Yucatan Peninsula has very few streams or ponds.  The primary source of water in the region has always been deep natural sinkholes that the Mayas called cenotes. Large Maya cities often developed near them.   Over time these natural wells would become inadequate for the population level, or inconvenient for many of the residents. To hedge against droughts,  architects designed enormous chambers under public plazas and buildings to store the rain runoff from the paved surfaces -- essentially, man-made cenotes. Some cisterns served the needs of remnant populations long after the civic centers were abandoned.  Some 1,000- to 1,500-year-old Maya cisterns are still in use today.   Application of the Cistern Concept to Metropolitan Areas   Recent headlines from across the United States point toward a growing crisis in the availability of potable water. Public reservoirs are going dry and ancient aquifers are being drained.  In the Southwest, the obvious cause is that populations have concentrated in desert and semi-desert regions: Under the best of circumstances, natural precipitation would be inadequate to meet the needs of the metropolitan areas. Local governments have no choice, but to build massive aqueducts from sparsely populated mountainous regions that experience heavy snowfall.   In the East the cause of water shortages tend to be more complex. In coastal areas, excessive pumping from deep underground wells is drawing brine water or sulfurous chemicals into the aquifers, making the water non-potable, or at least, unsuitable for human consumption. In other areas, the problems seem to be rooted in the lack of long-range infrastructure planning and inept administration of existing water resources.   Cisterns offer the most viable short-term solution to water shortages in the Eastern United States.  They utilize simple technology and relatively inexpensive materials.  Residential cistern systems can be installed and operating in a matter of a few days.  A major reservoir and 100-mile-long aqueduct for a metropolitan area could take 25 years to get into operation and cost hundreds of millions of dollars in land acquisition, design and construction.    Oh, there is one big drawback to cisterns, though.  Communitywide implementation of cisterns would not require the services of multi-office engineering firms or international construction conglomerates. How can politicians reward campaign contributors with such a simple solution?   On the other hand,  the fabrication of cisterns offers enormous potential business for locally owned companies that today manufacture septic tanks and concrete storm pipes. Underground gasoline tanks are also very suitable cisterns for potable water.  Widespread demand for cisterns also would create a healthy market for new manufacturing operations to start up. Those businesses, relatively small in size, would keep money at home rather than disperse it around the world as major contractors would do.   Strangely enough, most metropolitan regions have applied the concept of cisterns to storm-water management for over two decades, but they haven't gone the small extra step of providing hydraulic resources for potable water. Most metropolitan areas require all commercial, industrial, and institutional developments to construct storm-water retention basins, which store proscribed volumes of water during periods of excessive precipitation or snow melt.  Because they are typically surfaced with soil, during much of the year these basins become sterile, manmade marshes that breed mosquitoes and smell like cesspools.  Because the retained water contains petroleum-based residue from parking lots and toxic chemicals from commercially maintained landscapes,  the water becomes increasingly toxic to wildlife, and therefore, can not even be considered manmade wetland habitats.   Application of the cistern concept to creating dispersed hydraulic resources will require refinements of plumbing codes and existing storm-water retention standards. For cistern water to be suitable for human consumption, or even watering vegetable gardens, it must be drained from non-polluting surfaces.  Most roofs and decks are suitable catchment areas for potable water; parking lots and lawns are not.   Down-sized retention basins still would be necessary to control run-off from parking lots.  Use of cistern water only for washing clothes and watering lawns would require a dual water supply system and water pump. However, in reality, most rainwater is purer than the water coming out of metropolitan rivers, so with some modest treatment, say from an ultraviolet device, rainwater could be used throughout a house.   Benefits of Residential Cisterns   A typical house has at least 2,000 square feet of roof surface. In a region that gets 50 inches of rainfall (or melted snow) a year, that's enough to capture and store approximately 8,333 cubic feet or 62,333 gallons of water a year.  Thus, potentially a home could furnish itself 170 gallons of water per day.   Such a house would exert little or no demand on the municipal water system. It probably would be financially impractical for the house to sell water back to the system, however.   Benefits from Commercial Cisterns   A 100,000-square-foot neighborhood shopping center typically has about 120,000 square feet of roofing and walkway shed surfaces.  In a region with 50 inches of rainfall a year, the shopping center could store 500,000 cubic feet or 3,920,000 gallons of water.  Given that most shopping centers use substantially less water per square foot than homes,  they could actually become producers of potable water.  The same type tanker trucks that haul mountain spring water to commercial water bottling plants could be used to haul raw rainwater to municipal treatment plants.   Why have cisterns not been considered as solutions to metropolitan water shortages in the Southeast?  Good question. The first obvious problem is that cisterns would have to be installed on a metropolitan scale to solve a metropolitan water shortage.  Installation of a few hundred might reduce utility costs for their owners, but not make much of a dent on the regional shortage of potable water. Requiring new residences to contain cistern plumbing systems would add some to the cost of the house – about 75 percent of the cost of a septic system.   In retrofits of existing houses, a cistern would cost roughly the same as a septic tank system. When compared to the cost of constructing an entirely new water resource, the treatment facilities to handle it and the public employees to operate it, the operating costs of cistern seem like a bargain.   The initial obstacle, though, could well be cultural.  Whereas residents of the Shenandoah Valley are long accustomed to cisterns, those in other parts of the Southeast might be consider them to be a radical idea. But, then, maybe not. When given a choice between $100 a month water bills or a cistern, the cistern just might be a sweet alternative.   -- October 19, 2007