Water, water everywhere . . . and not a drop to drink. This famous line from the poem, “The Rime of the Ancient Mariner” is becoming an increasingly common complaint throughout urban areas of the United States. Too many water consumers are competing for usage for natural sources of water that are often polluted with dangerous chemicals from industries or storm water runoff from parking lots and farmlands. In drought prone regions, the line could be changed to water, water nowhere. Ancient underground aquifers and 20th century reservoirs are drying up.
A technology, almost as ancient as civilization itself, offers a solution to this growing national crisis. Its initial AND operating costs are far less than that required for urban water treatment & distribution systems, yet relatively few communities are currently implementing the solution. The concept can only be found in widespread usage in certain rural areas or in desert enclaves.
The solution is the construction of rainwater catchment cisterns that are incorporated into the buildings where the water will be consumed. In other words, structures would be designed or modified to collect the natural rainfall that falls onto the property, purify it and then store it in cisterns until the water is needed by the occupants of the building. In regions with moderate or heavy precipitation, it would also be possible for large commercial structures like shopping malls and parking lots to collect enough surplus water to service entire residential neighborhoods. The technology is actually less complex than that used to do to supply water from central treating plants. The main obstacle is apparently that governments are not encouraging rain cisterns, since no revenue would flow to their budgets from decentralized water collection.
A 250-year-old example, only an hour’s drive from the nation’s capital
Ironically, one of the most successful and time tested examples of rain cistern technology is only an hour’s drive away from the nation’s capital in the Shenandoah Valley of Virginia. The northern Shenandoah Valley is one of the driest regions east of the Great Plains. Most of its 28” of precipitation occurs during the winter and spring months. Most shallow wells go dry by mid-summer. The original settlers in the 1750s solved this problem by building brick masonry cisterns underground and channeling all the rainwater that fell on roofs into the underground cisterns. During the summer and fall, the cisterns function just like wells. Nowadays, if the cisterns go dry, the farmers purchase water from bulk haulers, who pump their water from mountain springs. However, when cisterns are connected both to home and barn roofs, farmers rarely need to purchase water.
Cisterns are still being installed for new rural homes in the Shenandoah Valley that are outside the jurisdiction of public utilities. Often the rainwater is filtered before entering the cistern. Periodically, homeowners will add water purification tablets to the prefabricated concrete tanks to cut down on the growth of yeasts and bacteria. The raw cistern water is used for washing clothes and vehicles – also watering gardens – while water, being piped to bathrooms and kitchens, first passes through a water purifier.
Native Americans Built Cisterns 2000 Years Ago
The concept of cisterns is an old one. The Mayas of the Yucatan Peninsula constructed enormous cisterns as their villages became cities. The Yucatan Peninsula has very few streams or ponds. The primary source of water in that region has always been deep natural sinkholes that the Mayas called cenotes. Large Maya cities often developed near cenotes. Over time these natural wells would become inadequate for the population level or inconvenient for much of the residents. To provide a hedge against droughts, Maya architects designed enormous chambers under public plazas and buildings to store the rain runoff from the paved surfaces. They were essentially man-made cenotes that were utilized in a similar manner. These cisterns often continued to serve the needs of remnant populations long after the civic centers were abandoned. Some 1000-1500 year old Maya cisterns are still in use today.
Application of the cistern concept to metropolitan area households
Recent headlines from several regions of 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 in desert regions have no choice, but to build massive aqueducts from sparsely populated mountains that experience heavy snowfall. In the East the causes 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, thus 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 solution to water shortages in many parts of the 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 might take 25 years to get into operation and cost several hundred million to over a billion dollars for land acquisition, design and construction.
The fabrication of cisterns offers enormous potential business for locally owned companies that today manufacture septic tanks and concrete storm pipes. Thoroughly cleaned, underground gasoline tanks are also very suitable cisterns for potable water. Widespread demand for cisterns would create a healthy market for new manufacturing operations to start up. Being relatively small operations, the money would stay at home rather than being dispersed all over the world as the case of major public works projects.
Strangely enough, the concept of cisterns has been applied to stormwater management for over two decades in most metropolitan regions, but not carried the slightly further step of providing hydraulic resources for potable water. Most metropolitan areas require all commercial, industrial, and institutional developments to construct stormwater retention basins, which will 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 infected, manmade marshes that function as breeding grounds for mosquitoes and smell like cesspools. Because the retained water contains increasingly higher levels of 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 stormwater 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 would still 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, rainwater could be used throughout a house.
How to retrofit your home to store rainwater
Most state health departments and county agricultural extension offices can provide you with standard plans for residential rainwater cistern systems. Some states have legal requirements for the approval of such systems; Others do not. You should check with your local health department to learn what might be required in your jurisdiction. Standard plans are also available off the internet as are web sites for companies that sell residential water system components. The following discussion will give you a basic concept of what is needed.
A typical house has at least 2000 sq. ft. of roof surface. In a region that gets 50 inches of rainfall (or melted snow) a year, approximately 8,333 cubic feet or 62,333 gallons of water a year could be stored by this modest sized home. Thus, potentially a home could furnish itself 170 gallons of water per day. There would no demand from this house on the municipal water system. In fact, there would be plenty of surplus water to irrigate the garden or sell to other consumers. A home with a larger roof area could harvest proportionately more rainfall. A home in a region with less average precipitation could harvest proportionately less rainfall from a given roof area.
Components: Most houses have gutters, so what you will definitely need are PVC plastic pipes with strainers to carry the water from the gutters to the cistern, and a water proof storage container sufficient in size to store all the water you need to get through a six week long drought. For most households in temperate climate zones, a 2000 gallon tank is sufficient. Those living in arid or semi-arid regions will need much larger storage capacity because for lengthy periods during the year, precipitation will be less than household consumption needs. A simple way to calculate the size of your cistern is to look at your monthly water bill. In regions with rainfall of 40 or more inches a year, just multiply the monthly consumption by 150%.
Roofing Materials: The ideal roof for a rain harvesting system is steel sheet roofing. This type of roofing does not retain debris and microbes like asphaltic and wood shingles. Asphaltic shingles also have the problem of gradually shedding tiny sand granules from their surfaces. A copper sheet roof is not desirable because acid rains would cause it to constantly shed trace amounts of copper and copper oxide, which can be toxic to humans and animals.
Purification: Although rainwater is typically far purer than surface streams, one can never tell when pathogenic microbes are floating around in the air. It is advisable, and often mandatory, in some states, to equip your catchment system with a water purifier. The most trouble-free method is the ultraviolet purifier. It does not require regular addition of chlorine and daily monitoring. However, your household system should have a backup purification system like that does not rely on electricity. Those thunderstorms which ended your community’s drought might also knock out the electrical power for awhile.
Maintaining Adequate Water Pressure: Municipal water systems create water pressure by using massive electric motors to pump water up into elevated tanks. Gravity then causes water to be under pressure as it flows from the elevated tanks to consumers. Of course, the rural version of this was the old time wind mill water pump that was not dependent on electricity. Wind mills are still being manufactured, but may not be desirable for your residence from a esthetic perspective, or not be permitted by zoning ordinances. Also, the construction costs of placing a 2000 gallon tank 20-30 feet up in the air, would drastically affect the economics of a residential water cistern system.
What is much more typical today is the placement of the cistern at an elevation slightly below that of the lowest roof gutter. Gravity carries the rainwater into the cistern. Water is then pumped from the cistern, under a desired pressure, by a small well pump. Above grade cisterns have an advantage over wells and below grade cisterns in that gravity would still force water into plumbing fixtures. However, some appliances like dishwashers, showers and clothes washing machines will probably not function properly if water pressure is not enhanced by an electric pump. Therefore, it would probably be advisable to invest in a backup generator, when electric power is not available.
Graywater Storage: Homeowners, who construct rainwater harvesting systems, often also install a smaller tank to store “Graywater” or the water flowing out of bath tubs and washing machines. This water, of course, is not potable, but can be used for watering gardens and washing cars. The tanks are typically 200 to 500 gallons in size. These graywater tanks are particularly common in arid regions where precipitation is deficient during the months when water is needed for small scale irrigation. They have also been utilized in prototypical “off the grid” houses that demonstrate the potential for houses to be completely independent of municipal and corporate utilities. An example of an “off the grid” house is illustrated in this article.
Construction Costs: Why have cisterns not been considered as solutions to metropolitan water shortages in the Untied States-? Good question. The obvious first 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 30% of the cost of a septic system with a drainage field. Retrofitting existing houses would probably be about 50% the cost of a septic tank system with a drainage field. Total investment for a three bedroom house would probably be in the range of $2,000 – $3,000.
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 cistern costs seem like a bargain. The initial obstacle, though, could well be cultural. Whereas residents of the Shenandoah Valley and the Great Plains are long accustomed to cisterns, those in other parts of the nation might be consider them to be a radical idea that seems “off the wall.” Well, then maybe not, when given a choice between $100 a month water bills or a cistern, the cistern just might be a sweet alternative.