Guide to Rooftop Water Tanks & Cisterns
InspectAPedia® -
Types of Rooftop water storage tanks
Rooftop cisterns
Rooftop water storage fed by municipal water supply or private wells and pumps
Pressure boosting pumps on gravity-operated rooftop water tank systems
Water storage tanks, cisterns, rooftop tanks, open tanks, water pressure tanks, steel tanks, range boilers, indirect-fired water heaters
Questions & answes about rooftop water tanks & cisterns
This article describes rooftop water tanks and cisterns, where they are used, how they work, and the use of booster pumps to improve water pressure in buildings with rooftop water storage tanks. We also discuss using a booster pump to improve building water pressure in buildings with weak municipal water pressure or a weak rooftop water supply system.
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Rooftop water storage tanks In some areas, Mexico, for example in our photo (above-left), rooftop water reservoirs are supplied intermittently with water
from a water main in the street. The rooftop water storage tanks in this photograph from San Miguel de Allende in Guanajuato are being used both to accumulate
a water reservoir so that water is always available to the building, and to supply water
at a useful pressure.
Our second photograph of a large rooftop water storage tank was taken in Manhattan. Rooftop storage tanks atop tall buildings have been in use for hundreds of years - this one was constructed of wood with iron bindings and is used to provide good water pressure to fixtures in the multi-story building it serves.
Rooftop Water Tanks or Free-standing Water Tanks at Ground Level
Rooftop water tanks in urban areas such as New York City may be used to supply water at high pressure to the
building below.
Water is pumped to the rooftop tank from its municipal source, then
redistributed at good pressure to the points of use in the building below.
When passing through
New York City, look at rooftops and you'll often see these tanks still in use. This sketch shows how
a rooftop tank might be constructed, though this particular sketch has the tank next to a well.
Plastic & Fiberglass Water Storage Tanks - HDPE Tanks
Reader Herman Voegel has pointed out that an up-and-coming area of storage containers includes spun-plastic tanks.
Specifically, new storage tank types include High Density Polyethylene (HDPE), currently available as tank storage for water, chemicals, waste oils, etc..
The plastic water tank in our photo (left) is used on ground level or on rooftops.
General HDPE containers come in all shapes and sizes and are quite rugged and relatively cheap compared to using typical 12-gauge steel home heating oil tanks.
The ruggedness of HDPE plastic containers comes from their material density which is typically at a minimum specific-gravity of 1.7, and for heavy-duty at 1.9.
These tanks may be used for storing certain liquids besides water. But home heating oil has not yet been approved for storage in HDPE tanks, basically for two reasons:
UV (ultra-violet) light degrading HDPE plastics over time, making them weak, and
Problems with slight permeation seepage through their plastic walls.
However, fixes have been put in place to properly address these problems. UV-light is checked by using special color additives that prevent their light from penetrating and degrading the plastic walls. Permeation or seepage of oil through container walls is checked by coating them with fiberglass.
Unfortunately, even with these fixes, HDPE plastics for heating oil storage have yet to be universally approved and accepted.
Readers should also see PLASTIC CONTAINERS, TANKS, TYPES where we describe health and other concerns involving plastic tanks and other containers used for water storage.
Attic Water Storage Tanks or Attic Cisterns
Attic Cisterns or water tanks are installed in some buildings
to perform the same function as rooftop-mounted water tanks.
Other smaller
attic containers that look like a water reservoir may have been just an
expansion tank for the heating boiler system.
Cisterns in basements or attics are an open-type water storage reservoir found indoors, and
are discussed further at CISTERNS.
A cistern was generally placed where it could be fed by gravity from roof or surface runoff, but any indoor open
topped reservoir of water could be called a cistern.
Water storage may not be on the rooftop nor in the attic. Cisterns or other water storage containers 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. See details at CISTERNS.
Rainwater Storage Tanks & Cisterns
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.
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.
The above-ground water cistern storage tank shown in our photo (left) is located in Mexico and is discussed at PASSIVE SOLAR HOME, LOW COST.
Rainwater for this cistern is collected from a near-flat rooftop and channeled to a large fiberglass holding tank - the blue tank in our photograph, (above left). Piping also permits directing water into this tank from a well-fed cistern located atop the concrete block tower). The tower's height provides water pressure to the building. Currently water is taken out of the bottom of this tank by a simple tank drain valve and hose attachment; to supply this water upwards to the building plumbing fixtures or perhaps to the cistern, a small electric pump will be installed.
See rainwater collection and storage cistern details at CISTERNS.
Water Pressure Boosting Systems
On low buildings or where the water tank is not high above the
point of use some systems install a water pressure booster pump and tank. A water pump (WATER PUMPS, TANKS, WELLS - BASICS) and probably a water pressure tank (WATER TANK BLADDERS & CAPTIVE AIR) will certainly be needed for ground-level or below-ground-level water storage cisterns.
Water pressure booster pumps and tanks may be installed in buildings where municipal water is supplied,
located on rooftops or anywhere in a building, so
don't assume that just because you see a pump and tank that the building is served
by a private well.
Water pressure boosting systems using a water pump and water tank are also installed
in homes where the municipal water supply pressure is low.
Readers of this document should also 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
and see Wells, Cisterns, & Springs for a discussion of types of drinking
water sources and what goes wrong with water supplies.
If you're looking for information on types of septic tanks see our Septic System Design which includes articles about various
types of septic tanks, steel, concrete, plastic, etc.
The illustration at page top is courtesy of Carson Dunlop, Inc. in Toronto.
Questions & Answers regarding this article
Questions & answes about rooftop water tanks & cisterns.
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Water Storage: Tanks, Cisterns, Aquifers, and Ponds for Domestic Supply, Fire and Emergency Use--Includes How to Make Ferrocement Water Tanks, Art Ludwig, Oasis Design (May 30, 2005), ISBN-10: 0964343363, ISBN-13: 978-0964343368, Quoting: A do-it-yourself guide to designing, building, and maintaining water tanks, cisterns and ponds, and sustainably managing groundwater storage. It will help you with your independent water system, fire protection, and disaster preparedness, at low cost and using principles of ecological design. Includes building instructions for several styles of ferro cement water tanks.
Thanks to aerospace engineer Herman Vogel, July 2010,
for providing an update on High Density Polyethylene HDPE storage tanks for water, chemicals, waste oils, etc.
Smart Tank, Installation Instructions, Flexcon Industries, 300 Pond St., Randolph MA 02368, www.flexconind.com, Tel: 800-527-0030 - web search 07/24/2010, original source: http://www.flexconind.com/pdf/st_install.pdf [Copy on file as /water/Smart_Tank_Flexcon.pdf ] -
Typical Shallow Well One Line Jet Pump Installation, Grove Electric, G&G Electric & Plumbing, 1900 NE 78th St., Suite 101, Vancouver WA 98665 www.grovelectric.com - web search -7/15/2010 original source: http://www.groverelectric.com/howto/38_Typical%20Jet%20Pump%20Installation.pdf, [Copy on file as /water/Jet_Pump_Grove_Elect_Jet_Pumps_1.pdf ] -
Typical Deep Well Two Line Jet Pump Installation, Grove Electric, G&G Electric & Plumbing, 1900 NE 78th St., Suite 101, Vancouver WA 98665 www.grovelectric.com - web search -7/15/2010 original source: http://www.groverelectric.com/howto/38_Typical%20Jet%20Pump%20Installation.pdf, [Copy on file as /water/Jet_Pump_Grove_Elect.pdf ] -
Cooperative Extension, School of Forest Resources, web search 07/24/2010, original source: http://pubs.cas.psu.edu/FreePubs/pdfs/XH0002.pdf
Water pressure tanks - how to diagnose the need for air, how to add air, stop water pump short cycling to avoid damage - water storage water pressure tank safety.
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