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This article describes water tanks and other kinds of tanks found in buildings, captive air and traditional water storage tanks or water pressure tanks, and we provide advice about what to do when things go wrong, such as finding air and water leaks or deciding to replace a water tank. 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 ourSeptic 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.

© 2009 Daniel Friedman, All Rights Reserved. Information Accuracy & Bias Pledge is at below-left. Use links at the left of each page to navigate this document or to view other topics at this website. Green links show where you are in our document or website.

Various types of tanks uses in and around buildings are identified and explained below, including water pressure tanks, water storage tanks, range boilers for hot water, indirect fired hot water tanks, expansion tanks in attics, basements, and on heating boilers, oil storage tanks, rooftop tanks, cisterns, water pressure booster systems. We also discuss when to replace water tanks.

Types of residential water tanks

CAPTIVE AIR TANKS bladder-type water tanks for Building Water Pressure Regulation

Newer "captive air" tanks use a rubber bladder to keep water and air separate. This prevents the air charge from being absorbed into the water, so you should never need to add air to those systems. At WATER TANKS HOW THEY WORK we provide details of how water pressure tanks work.

Loss of air in "captive air" bladder type water pressure or water storage tanks

If a "captive air" or internal "bladder" (usually rubber) type tank is installed, and if the pump is short-cycling on and off, you should turn off the pump and call a plumber.

We would suspect that the bladder has ruptured, or that the tank itself has developed a leak. We explain waterlogged water tanks and water pump short cycling in detail at WATER TANK REPAIRS where we also explain how to correct these conditions.

Regardless, short cycling could damage the pump or pump controls. These tanks are made of steel or fiberglass, and typically have an air schrader valve at the top of the tank. The air valve is used for adjustment of the air pressure in the tank at the time of initial installation. Normally you never need to add air to these tanks after initial installation. Sketch courtesy of Carson Dunlop.

The newer type "captive air" tanks, one which use an internal bladder to contain the water separately from the air charge, can also fail. The bladder can rupture as we discussed above - you need a new tank. The tank itself can develop an air leak - you need a new tank. But these failures occur less often than with the older single chamber steel water pressure tank, largely because the tank bladder holding the water supply protects the tank interior from corrosion.

On some captive air water tanks this design is reversed. For example on the WellMate™ water tank the water is in the tank and air is in the tank bladder. This difference can confuse the burst water tank bladder diagnosis procedure which we describe below. At WellMate Diagnosis we provide separate water tank diagnosis and repair advice.

If the captive air water pressure tank bladder is ruptured, the air charge in the tank becomes lost over time and the tank acts like a water-logged steel tank discussed below.

If the captive air water pressure tank bladder is collapsed,, defective, jammed, and stuck on itself it may not accept much volume of water, also leading to a short draw-down cycle before the pump has to turn on again. This is an unusual case but has been reported to me on occasion.

Bladderless Fiberglass Water Pressure Tanks, such as the WellMate traditional hydro-pneumatic water tank operate similar to the steel water pressure tank, that is, no internal bladder is used to maintain and separate the tank's air charge and water charge pressure. These tanks incorporate a tank-top mounted air volume control and offer the advantage (over steel water tanks) of no risk of rust perforation and leak at the water tank. At WellMate Diagnosis we provide separate water tank diagnosis and repair advice for this water tank type.

OLDER STEEL TANKS - Bladder-less Traditional Steel Water Pressure & Water Storage Tanks

There may be lots of kinds of tanks found in buildings, storing water, fuel, hot water, or serving other purposes. We review quite a few of them here and include photographs to help you figure out what's what.

Steel Water Storage/Pressure Tanks

The water storage tank in the photographs above is leaking, having rusted through from inside the tank. (This tank is less needed for storage than to smooth or regulate the water pressure in the building as the pump cycles on and off) Leaks like the ones in these photos can also leak the air charge out of the upper portion of the tank when the in-tank water level is below the leak point. So you might trace a water pump short cycling problem to an air loss in the tank to a leak in the tank itself.

How to detect a waterlogged water tank

If a steel water tank has lost its air charge, or most of it, the condensate line on the tank will be high, near the top few inches of the tank side (unless you live in an arid climate where there is never condensation on the water tank anyway.). Sketch courtesy of Carson Dunlop.

In this condition the steel tank is called a waterlogged water pressure tank. Such tanks will also be heavy and won't be so easily rocked or moved - a simple test we make to see if the tank is empty or full of water. (Don't move the tank so much that you cause a water piping leak!

When to add air to a water tank

The discussion on how to add air to a water pressure tank at this website beginning at HOW TO ADD AIR applies principally to older steel water tanks that don't use an internal bladder to keep water and air separate.

In these simpler single-internal chamber steel tanks the air charge is lost either by absorption into the water as it passes through the tank during use, or it may be lost by leaks at the tank or nearby plumbing fittings.

Automatic ways to add air to a water tank

Some old-style bladderless steel water pressure tanks are equipped with an air volume control device which is intended to put makeup air into the tank as air is lost or absorbed. I discuss these further at 1: AIR VOLUME CONTROLS but suffice it to say these often stop working. But if you see one on your water tank you know this is a non-bladder type older style water pressure tank.

Range Boilers for Domestic Hot Water Systems

Range boilers are vertical or horizontal hot water systems whose water is heated by circulating the water from within a water storage tank (the range boiler) through a heat exchanger which is inside or connected to the exterior of a heating boiler. The water in the hot water tank range boiler is heated by circulating its water through the heat exchanger which itself is heated by the water inside or from the heating boiler.

The sketch illustrates how a very early type of coal-fired water heater range boiler worked. As homeowners shifted fuels from coal to oil or gas and installed central heating boilers, often the range boiler water heater was adapted to work with these systems as well, as you can see in the photograph.

As with the indirect-fired boiler described next, range boiler water heating tanks are usually located close to the heating boiler and will have both cold and hot water lines leaving the tank to supply the building with domestic hot water and a loop of piping that runs between the bottom of the hot water tank and a nearby heating boiler. Follow the pipes to see which pipes are performing which function. Our photo shows a silver steel range boiler hiding back in the corner behind the newer (though pretty old) gas fired water heater. (Notice also the efflorescence on the masonry block foundation, where the downspout has been spilling by the house foundation?)

See WATER HEATERS for details about residential hot water systems.

Indirect-Fired Domestic Hot Water Tanks

Indirect fired water heaters: In some other buildings domestic hot water is produced by cycling hot water from a hydronic or steam boiler through a loop inside of a steel tank. The water in the tank is heated by the water in the coil. Modern systems using this approach use the term indirect-fired water heater and such systems are sold by various companies such as the SuperStorTM unit shown here as the white tank to the right of the heating boiler. You may also notice the WellXTrolTM blue water tank off to the left of the boiler as well as in the left foreground covered partly by a cardboard box we have a white-yellow fiberglass close to the thin blue vertical water softener - water treatment equipment in the same photo. And just to be complete, the little tank over the boiler next to our service technician is the expansion tank for this heating boiler. Indirect fired water heater tanks for domestic hot water, such as the SuperStorTM are usually located close to the heating boiler and will have both cold and hot water lines leaving the tank to supply the building with domestic hot water and a loop of piping that runs between the [usually the] bottom of the tank and a nearby heating boiler. Follow the pipes to see which pipes are performing which function.

The difference between a range boiler and an indirect fired water heater is in the details. The heat exchanger that heats water in the range boiler is in or at the heating boiler. The water in an indirect fired water heater such as the SuperStor^TM unit is heated by a finned copper coil located inside the hot water tank. The internal coil is in turn heated by circulating water inside the coil to and from the heating boiler. The range boiler is an old concept in use for about 100 years. Indirect fired water heaters are a modern system and are in current sales and use.

See WATER HEATERS for details about residential hot water systems.

Attic Expansion Tanks for Heating Boilers

Attic expansion tanks and pressure relief systems for boilers: Don't confuse an old heating system attic-mounted expansion tank like the one shown here for a water tank storage tank. 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. This attic expansion tank may have been connected to a drain that spilled outside of the building in case the tank became over-full. You can also see a sight glass on the front of this tank, allowing the service person to see its conation. Don't confuse this little tank with a water storage tank, nor with the larger range boiler tanks discussed here. Heating systems with this equipment installed may not have a modern pressure and temperature relief valve. Certainly in the original design the tank was put in the attic so that heating water could rise to the upper floors of the building by pressure within the heating system, but if pressure got dangerously high, heating boiler water would just spill up into the attic and thence to outside. Systems which rely on a remote attic-mounted expansion tank are less safe since than a boiler that has a pressure and temperature relief valve mounted right on or at the boiler. It's an easy fix, usually, to just add a relief valve on or at the boiler.

Basement Expansion Tanks for Heating Boilers

Our client is pointing to a do-it-yourself insulating job on a water heater. But that reddish-brown horizontal tank over his head is an expansion tank for the hydronic heating boiler in this building. This is not a water storage tank, it's not a range boiler, it's an expansion tank. There will usually be just one pipe leading to this tank, coming from the boiler or perhaps a nearby heating water pipe to the tank to permit it to accept the expansion of water in the heating system (or expanding air entrained in the heating system's water) as the boiler gets hot. Otherwise the boiler relief valve might open and spill every time the boiler went through a heating cycle. You'll also find a drain on the bottom of this boiler, used by the heating service technician. So unlike the attic expansion tank, this basement expansion tank is expected to be on a heating boiler that also has a pressure and temperature relief valve.

Oil Storage Tanks in Buildings

This is a typical indoor oil storage tank in a residential building. We have a lot to say about oil tanks in buildings, oil tank leaks, environmental risks, potential costly cleanups, and effects of oil tank problems on the heating system and its operation. For information about oil tank issues and solutions see Heating Oil Underground & Above ground Oil Storage Tank Leaks, Testing, Problems & Solutions, Home Buyer's / Home Owner's Guide. These online articles answer most questions about above ground or buried oil storage tanks. What's really important in this photo is the black wall-mounted gauge our client is pointing to. He's found an indication that there is or was a buried underground oil tank at this property - potentially a costly environmental problem if that tank leaked. Given the leakage all over the old oil tank that we can see indoors in this photo, we weren't too optimistic about what might have happened with an old outdoor buried tank. Some testing was ordered.

LARGE WATER TANKS - Large Water Storage Tanks, Why They Are Used, What They Imply about Well Recovery Rate or Well Yield

Very large water storage tanks, such as the one whose end is visible in these photographs from two different properties, are likely to indicate that the flow rate of the well serving the property is very slow, even inadequate by contemporary standards.

We've found these old steel tanks at older properties in the Northeastern U.S. in situations where the well flow rate, the rate in gallons per minute at which the well can give water over a sustained period, to be very low, perhaps around one gallon per minute or less. Very low well flow or well water delivery rates in the 2.5 gpm range or below, simply can't keep up with the rate of water usage in a building during normal occupancy.

Large water tanks may indicate that the well flow rate can't keep up with demand

Worse, if we have only a typical water tank installed, say a 30 or 40-gallon unit, that tank is designed to smooth the flow of delivery of water to the building as the pump is turned on and off. A small water tank is not sized to actually store a reservoir of water for the building. So if our well flow rate is very low, the building will simply run out of water and occupants will have to wait, perhaps hours, for the pump to re-fill the water tank.

A low flow rate well and pump may rely on "recovery" overnight or over many hours

So a common solution for a low-flow-rate well is the installation of a very large water reservoir. At older properties the single water tank may have been 1000 gallons or even more. With a large water tank installed to provide this water storage reservoir, the well flow rate can be terrible but the building occupants won't see its effect since they're working off of the water storage tank.

At a low-flow-rate well installation the pump will be designed to run at a slow pumping rate so that the well water flow-rate can keep up with the pump as the pump sends water to the water storage tank. The building occupants use water out of the tank and the tank and well and pump recover their water slowly, perhaps overnight.

Low flow rate wells or slow recovery rate wells at modern properties use a cascade of water tanks

At newer properties this same approach may be taken to "solve" a low-flow well but instead of a single huge steel tank such as the one in this photograph, the plumber will install a series or cascade of from two to perhaps four or five smaller water storage tanks of perhaps 50 gallons each. If you are looking at a property and see that it has five new shiny blue and pretty big water tanks lined up in the basement you can guess that the well is marginal in its delivery capacity.

Low flow rate slow recovery rate wells have a questionable future life expectancy

A final warning about low-flow rate wells: because in many areas water is flowing into the well through cracks in rock below the surface, and because we're starting with an already low recovery rate well, the future ability of the well to give water at all must be questioned. If local water is heavy in minerals, for example, the minerals tend to clog up those rock cracks over time, gradually reducing the water flow-rate into the well still further, until eventually it just stops working.

So a very large water storage capacity at a property is an indicator of both a low-flow-rate well (poor well recovery rate means the same thing), and an indicator that the future usability of the well at all must be questioned. We explain how people determine the necessary water tank size and volume at WATER TANK SIZE & VOLUME .

OPEN WATER TANKS - gravity fed water systems or pump-up rooftop systems with and without pressure-boosting pumps and water tanks

Rooftop Water Tanks or Free-standing Water Tanks at Ground Level

Rooftop Water Storage Systems

Open Water Tanks Indoors

At some locations there is an up-hill or rooftop water source which is fed into the building entirely by gravity. The open top water tank in these photos used a simple float valve to let water into this storage tank. Where such intermediate storage tanks, perhaps fed by an uphill spring, were located in the upper floors of a building they fed water to building piping where it could flow by gravity when a water tap was opened.

Cisterns for Water Storage

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.

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.

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. 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.

Water Pressure Boosting Systems

WHEN TO REPLACE WATER TANKS - When do you need a new water tank?

When an older type (non-captive-air) tank needs replacement (for example because it has rusted through and has perforations leaking water or air, or if adding air frequently becomes a hassle, you'll want the newer type of "captive air" or "bladder" tank. If your tank looks like it has leprosy, if you see water streaming down its side from a "pinhole" leak, it may be possible to make a temporary emergency repair using a rubber washer and screw. Your hardware store sells special screws for this purpose. This is only a stopgap measure. You need a new tank.

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• Daniel Friedman - principal author/editor of the InspectAPedia^® Website
• Critique, contributions wanted: Contact Us to suggest corrections or additions to articles at this website, and if you wish, to receive online listing and credit as a contributor. Particular thanks are due to the many experts and also consumers who read and critique technical articles at InspectAPedia.com.
• Thanks to Alan Carson and Bob Dunlop, Carson Dunlop, Associates, Toronto, for permission to use illustrations from their publication, The Illustrated Home which illustrates construction details and building components. Carson Dunlop provides home inspection education, publications, report writing materials, and home inspection services. Alan Carson is a past president of ASHI, the American Society of Home Inspectors.
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• Water pressure tank failures & water pump short cycling diagnosis and repair
• Cheating on water tests: Testing Water for Real Estate Transactions - make sure your water test is valid
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