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 How to Prevent Water Accumulation in Oil Storage Tanks
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Prevent water contamination in heating oil storage tanks: this article explains how to keep water out of oil storage tanks, both buried tanks (USTs) and above ground storage tanks (ASTs). This article series explains the problems caused by water accumulation in oil tanks, how water gets into the oil tank, how to measure water in the oil tank, how to remove water from oil storage tanks regardless
of whether the oil tank is indoors, outdoors above ground, or buried, and how to prevent water from getting into an oil storage tank. We explain how to test for or visually check for water in a buried or above-ground oil storage tank, and how to get water out of an oil tank.
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How to Keep Water Out of Oil Storage Tanks
Tips for Keeping Water out of a Buried Oil Tank
This website provides detailed information about underground (buried) oil storage tanks (USTs),
aboveground oil storage tanks (ASTs), above ground fuel storage tanks, reporting and cleaning up oil tank leaks, and choosing among oil tank leak testing methods. We include detailed information about underground (buried) oil storage tanks (USTs),
aboveground oil storage tanks (ASTs), above ground fuel storage tanks, reporting and cleaning up oil tank leaks, and choosing among oil tank leak testing methods.
Home buyers should be sure to review OIL TANK TESTING - Leaky Heating Oil Tanks - How Oil Tanks are Tested for Evidence Leaks, of Current or Previous Oil Spills
and Tank Legal Issues - Home Buyers and Home Owners Guide to Leaky Heating Oil Tanks - What to Do About & When to Report Oil Tank Leaks. Leaky Heating Oil Tanks.
Home owners who have old oil tanks above ground or any age oil tank below ground should also be sure to review OIL TANK ABANDONING PROCEDURE - Abandoning Commercial vs. Residential Underground Oil Storage Tanks (UST) - Procedures & Regulations
A separate website addresses Septic Tanks.
- Water enters a buried or above ground tank by condensation: as temperatures vary moisture-containing air may be drawn into and then out
of an oil tank.
Air leaves the tank as oil is consumed; air enters and leaves the oil tank through the oil tank vent. Moist air entering the tank
from outside can bring water which, on entering the cooler tank interior, condenses out of vapor form into water droplets which can, over time
accumulate.
- Water enters a tank filler pipe: from roof spillage onto the tank or filler top (particularly and obviously if the filler cap is left off),
or from ground or surface runoff entering the oil storage tank (particularly and obviously if the filler cap is near, at, or below ground surface level).
- Leaving off an outside oil tank filler cap for a few days is not itself a likely source of a problem unless the filler
was exposed to heavy rain, roof runoff spillage onto the open filler pipe, or surface runoff entering the tank
(such as for a filler pipe flush with the ground).
- Water leaks into a buried oil tank from an actual tank perforation that admits ground water, or from a bad plumbing fitting on the tank. When oil levels in the tank is below an oil tank perforation or a leak in oil tank piping, it is possible for ground water to leak into a buried oil tank just heating oil may leak out of the oil tank when it is filled above the perforation or leak point.
- Water leaks into the buried oil tank from a faulty filler cap gasket around the oil tank filler pipe plug, especially at installations whose oil tank filler pipe is located in a box whose top is flush with the ground surface.
Rainwater or snow-melt water then enter the oil storage tank. The buried oil tank illustration (left) is provided courtesy of Carson Dunlop Associates. You'll notice that the oil tank is sloped away from the tank bottom oil piping connection, as we discuss below.
- Water leaks into the buried oil tank from an oil tank vent pipe that is missing a cap to protect against rainwater or roof runoff spillage into the tank, especially if the vent (or filler pipe) are located under the roof's drip-line.
- Water leaks into a buried oil storage tank from leaky oil piping fittings. R.W. Beckett recommends that [Quoting]
All pipe fittings must be tightened securely and have the threads sealed with a resilient compound that can endure the environmental variables in temperature. Any loose or poorly sealed [oil tank fuel piping, fill, or vent piping] joints can permit ground water to infiltrate the [oil] storage tank.
- Water is delivered to the oil tank along with the heating oil fuel: This is not common, but it is possible to get a delivery of "bad" heating oil that is water contaminated,
especially if the oil truck happens to fill-up at the oil storage depot when an oil barge is
unloading oil since during that operation water which is normally kept in the bottom of oil depot
storage tanks may be stirred-up.
Most oil companies know to avoid this problem and some also have water
filters installed at their oil trucks. No oil company is going to admit that they picked up and delivered
water-contaminated oil to your home so don't waste time asking them if they are guilty of this crime.
R.W. Beckett referred to this [quoting] "possible but rare contributor due to storage and maintenance practices in the [heating oil] distribution system. Large bulk [oil storage] tanks must be checked for condensation accumulation and bled periodically.
If this is not done conscientiously, then it is possible for water to be drawn out with the oil when the stocks are extremely low or when the bulk storage is filled and the water is forced into temporary suspension. Fortunately, our industry has implemented effective maintenance measures and this has been virtually eliminated. However, if water and sludge are found in a tank that does not have a leak, then it must be thoroughly pumped out, cleaned, and treated with a chemical additive that disperses water, sludge and neutralizes bacterial growth."
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Tips for Keeping Water Out of Above Ground Oil Tanks
As we discussed at How Water Gets in Above-Ground Oil Tanks Sources of water entry into above ground oil storage tanks are similar to the UST water leak sources listed at How Water Gets in Buried Oil Tanks. [Paraphrased, edited, and expanded from R.W. Beckett] :
- How to avoid condensation inside outdoor above ground oil storage tanks: Also as we discussed at How Water Gets in Above-Ground Oil Tanks, Outdoor above-ground oil storage tank water condensation occurs when a partially-filled oil tank is exposed to variations in outdoor temperature. Oil in the tank and the tank steel itself are warmed by sunlight and higher daytime temperatures.
[Items below are paraphrased, edited, and expanded from R.W. Beckett and other sources]:
Paint the above-ground outdoor oil storage tank silver (aluminum paint) to reflect sunlight (and heat), or locate the tank in a shaded area if possible. If you consider that in freezing climates we recommend constructing a heated enclosure around an outside oil storage tank to avoid oil tank waxing or water freezing and loss of heat, that step will also reduce the problem of oil tank water accumulation due to condensation.
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- Install properly sealed fill and vent pipes on the oil storage tank, and avoid locating the tank where roof runoff spills onto the tank or its piping (see our oil tank photo at left).
- Install the oil tank so that the oil tank fill pipe end is sloped downwards. This will cause water entering at the fill pipe to pool right below the filler cap where it can be observed and pumped out.
- For oil tanks drawing oil from the oil tank bottom, install a 3" vertical riser (soldering a 3" x 1/2" O.D. copper tube) onto the oil tank side of the oil tank bottom fitting so that oil is always drawn off from 3" above the tank bottom, thus above water that may be accumulated on the oil tank bottom (as long as the water has accumulated to a level less than 3" this works).
- Install a water tank drain port on the lower end of the above-ground oil storage tank. [Properly installed a aboveground oil tank is installed with a few inches of slope away from the tank bottom outlet fitting so that water and sludge accumulate first away from the oil supply piping connection point.
Even if the oil piping is installed through the tank top fittings (a better, more water and sludge-resistant approach), an oil tank bottom drain can still be used to check for and remove water accumulated on the oil tank bottom.
- Install the oil supply and return piping through oil tank top fittings rather than at the oil tank bottom fittings.
A 3/8" or 1/2" diameter compression fitting is installed in a special dual-port oil tank top fitting that permits the copper oil supply and return piping to be routed through the tank top fitting, extending continuously (without potentially leaky joints) to 3" above the oil tank bottom. (See our photo at left.)
R.W. Beckett's illustration shows that the oil pickup and return tubing are also bent at an angle away from one another so that the oil pick-up line does not pick up sludge or air bubbles that are caused by excess oil returning to the oil tank through the oil return line.
- Keep the heating oil tank filled during warm weather. By minimizing the air space above oil in the oil storage tank you will reduce the oil tank air "exhale" as the oil tank warms, and "inhale" as the oil tank cools, thus reducing outside air and moisture being drawn into the oil tank.
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Technical Reviewers & References
Related Topics, found near the top of this page suggest articles closely related to this one.
- "Preventing Water from Entering the [oil heating] Fuel System", Technical Information Bulletin, 10/15/1990, R.W. Beckett Corporation, 38251 Center Ridge Road, PO Box 1289, Elyria OH 44036, Tel: 440-327-1060, Email: sales@beckettcorp.com
 Carson, Dunlop & Associates Ltd., 120 Carlton Street Suite 407, Toronto ON M5A 4K2. (416) 964-9415 1-800-268-7070 info@carsondunlop.com. The firm provides professional home inspection services & home inspection education & publications. Alan Carson is a past president of ASHI, the American Society of Home Inspectors. Thanks to Alan Carson and Bob Dunlop, for permission for InspectAPedia to use text excerpts from The Home Reference Book & illustrations from The Illustrated Home. Carson Dunlop Associates' provides:
- Commercial Building Inspection Courses - protocol ASTM Standard E 2018-08 for Property Condition Assessments
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- Home Inspection Education Home Study Courses - ASHI@Home Training 10-course program.
Special Offer: Carson Dunlop Associates offers InspectAPedia readers in the U.S.A. a 5% discount on these courses: Enter INSPECTAHITP in the order payment page "Promo/Redemption" space. InspectAPedia.com editor Daniel Friedman is a contributing author.
- The Home Reference Book, a reference & inspection report product for building owners & inspectors.
Special Offer: For a 10% discount on any number of copies of the Home Reference Book purchased as a single order. Enter INSPECTAHRB in the order payment page "Promo/Redemption" space. InspectAPedia.com editor Daniel Friedman is a contributing author.
- The Home Reference eBook, an electronic version for PCs, the iPad, iPhone, & Android smart phones.
Special Offer: For a 5% discount on any number of copies of the Home Reference eBook purchased as a single order. Enter inspectaehrb in the order payment page "Promo/Redemption" space.
- The Illustrated Home illustrates construction details and building components, a reference for owners & inspectors.
Special Offer: For a 5% discount on any number of copies of the Illustrated Home purchased as a single order Enter INSPECTAILL in the order payment page "Promo/Redemption" space.
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Books & Articles on Building & Environmental Inspection, Testing, Diagnosis, & Repair
 The Home Reference Book - the Encyclopedia of Homes, Carson, Dunlop & Associates Ltd., Toronto, Ontario, 2010, $69.00 U.S., is available from Carson Dunlop, and from the InspectAPedia bookstore. The 2010 edition of the Home Reference Book is a bound volume of more than 450 illustrated pages that assist home inspectors and home owners in the inspection and detection of problems on buildings. The text is intended as a reference guide to help building owners operate and maintain their home effectively. InspectAPedia.com ® author/editor Daniel Friedman is a contributing author. Field inspection worksheets are included at the back of the volume.
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- National Association of Oil Heat Service Managers, PO Box 380, Elmwood Park, NJ 07407
- "Homeowners Guide to Fuel Storage," Agway Energy Products, Verbank, NY, November 1990
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