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This article describes the use of cisterns as drinking water sources. We provide advice about what to do when things go wrong. Readers of this document should also see Water Tank Types and before assuming that a water problem is due to the well itself, see Water pump and pressure tank repair diagnosis & cost an specific case which offers an example of diagnosis of loss of water pressure, loss of water, and analyzes the actual repair cost.

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Cisterns and How to use them for Drinking Water Storage

A cistern is basically a water reservoir of any kind which is used to accumulate and store water for future use. Cisterns are usually constructed close to the building which will use their water, sometimes even inside it. Traditionally and still in some parts of the world people direct roof runoff from the rainy season into a cistern where it is stored for use during dry periods.

Water from a cistern is typically pumped out by hand, drained by gravity, or it may be pumped by an electric pump such as a one line jet pump. The photo at page top shows an abandoned cistern which had been built abutting a home. Interestingly the owner broke through into the cistern from the basement and drilled a modern steel casing well right in the bottom of the cistern - some of the new equipment is also visible.

Cisterns to store water for drinking or agricultural purposes are widely used in dry areas where rainwater runoff may be stored for future use. However all water storage cisterns that are to be used for drinking or potable water supplies are at risk of contamination either from external sources or from bacterial growth during the water storage interval.

Basement & Outdoor Cisterns, are often located in the basement or courtyard of buildings where they collect rainwater for future use. In the U.S. cisterns were often located in the basement of a (pre-1900) home. In arid areas such as the U.S. Southwest and parts of Mexico, very large cisterns are often placed in a courtyard where they collect rainwater for use during the dry season. This cistern is located in the basement of a pre-1900 home in New York. Later owners broke open a passage into the basement cistern and now use it for storage. This cistern was originally filled by downspouts directing roof runoff into the basement.

Cisterns in older buildings can be tricky to spot - the cistern may have been partly demolished, such as in photos shown above, or the cistern may be a walled structure whose top is just below the joists of the building's first floor, as we see in the photos just below. A tip that led to our discovery of this cistern was an unexplained drainpipe protruding to outside through a building wall. We traced the drain to a nearly-hidden basement cistern where it handled cistern overflow.

In a seasonally damp climate such as New York, an in-use basement cistern would certainly be a likely source of unwanted building moisture and would thus be a risk for problematic mold growth.

Advice for using Cisterns for Water Supply

• Safety: be sure the cistern is of sound construction and that it is safely covered or protected from someone falling into the cistern or from a child climbing into it.
  
  
• Direct roof runoff, not surface runoff, into the cistern. Some clever roof runoff management systems direct the first roof runoff onto the ground, permitting dust and debris from the roof surface to be disposed-of before the remaining roof runoff is directed into the cistern for water storage. Other water sources may be used to supply cisterns, including even local or municipal water supplies. In this case the cistern is being used as a backup or off-peak water supply source.
  
  
• Do not assume that water stored in a cistern is potable prior to filtering and treatment. The water should be tested for contaminants before used for drinking; it's fine to use cistern water for watering plants or lawns if that water usage is suitable and permitted by other conditions.
  
  
• Do not install an open, un-covered cistern in a building where moisture from the cistern could cause a mold or rot problem.
  
  
• Provide access to the cistern for inspection and cleaning
  
  
• Pumps for cisterns: if you intend to rely on an electrical pump to move water from the cistern to its point of use during bad weather and possible power outage your pump will need a backup source of electricity.

Attic Cisterns or water tanks are installed in some buildings to perform the same function as rooftop-mounted water tanks. This little attic reservoir found in the Justin Morrill historic home.

Attic expansion tanks and pressure relief systems Don't confuse an old heating system attic-mounted expansion tank for a water tank however. These are not potable water storage systems. The heating system expansion tank will be connected to the heating system radiators or basement boiler and may have a simple overflow pipe to permit excessive water (or system pressure) to spill outside. Heating systems with this equipment installed may not have a modern pressure and temperature relief valve. Attic expansion tank systems used on heating boilers are potentially less safe than installing a relief valve right on the boiler, since the attic-located pressure relief system is located so remote from the heating boiler.

Is a Cistern an Acceptable Water Supply for HUD Financing?

Cisterns:HUD Handbook 4150.2 Section 3-6 indicates that properties served by cisterns are not acceptable for mortgage insurance. However, the HOCs have the authority to consider waivers in areas where cisterns are typical.

Our photo (above left) shows a hybrid system: this outdoor cistern is filled by pumping from an open casing in a drilled well that was inserted in the bottom of a dug well that went "dry" (photo, above right).

As will be apparent to readers, both the open top of this cistern and the open casing in the bottom of the dug well are sources of water contamination.

See WELL CLEARANCE DISTANCES for more information about cisterns, well and water source clearances from potential pollutant sources, and possible exceptions that can permit use of cisterns for drinking water supply.

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