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Learn About 5 Common Failures That Cause Water Damage in Residences

The old adage of "prevention is the best medicine" applies to more than just healthcare

Published: June 2, 2020

By: David C. Neidig, B.Sc.

We have engineers who specialize in determining the origin and cause of water losses.  Knott Laboratory has years of experience performing site inspections and laboratory testing.  In these times of stay at home and stay safe, the old adage of “prevention is the best medicine” applies to more than just healthcare.  With more people spending time at home, now is a good time to consider loss prevention and Knott Laboratory engineers have five commonly observed failure locations to look for around the house.

1. Flexible Supply Lines


Most residential fixtures and appliances use rubber, plastic, or braided stainless steel jacketed flexible supply lines to connect to the home’s permanently installed plumbing system.  Knott Laboratory has examined supply lines from dishwashers, washing machines, refrigerators, water filters, water heaters, faucets, and toilets.   This value is based on typical service conditions and is designed to replace worn items before they fail.  The life expectancy of a supply line may be drastically affected by such things as: water chemistry, external chemical exposure, water pressure, and physical damage.  Consider inspecting all your supply lines for typical signs of degradation including cuts, nicks, gouges, cracking, blistering, damp spots/drips, or corrosion.

Did you know – Many manufacturers provide a recommended service life limit for flexible supply lines and often suggest replacement every five years?

Easy to correct, and often overlooked areas to consider are:

  • Faucet/Dishwasher Supply Lines: These lines are typically enclosed in a cabinet and are out-of-sight which makes dampness and drips easy to miss.  These locations are also frequently used for storage of household cleaning agents, which can be detrimental to the life expectancy of a supply line.  The cleaning agents can chemically attack the supply line from the outside as natural evaporation occurs and an over-crowded storage space may result in physical damage to the lines.
  • Toilet Supply Lines: Toilets utilizing a supply line with a plastic ballcock nut may be at a higher risk for a future water loss. These fittings are typically designed to be hand-tightened to the toilet fill valve connection.  Over tightening during installation may be one factor that leads to creep failure of the plastic nut.  In some homes, plastic nuts made using acetal, typically characterized by a translucent white appearance, are especially susceptible to degradation due to chemical embrittlement and physical stresses.
  • Refrigerator/Water Filter Supply Lines: These lines are often plastic and use push-to-connect fittings or compression nuts.  As with faucet lines, they are frequently located in out-of-site areas and they are rarely inspected.  Common modes of failure are embrittlement (cracking) from chemicals in the water or a nearby heat source, or stress from physical damage such as pinching or bending.


2. Water Filters


Typical residential water filter applications are point-of-entry (POE) and point-of-use (POU). POE systems are typically located at or near the water supply entry for the home and are intended to condition the water for the entire residence. Typical failures associated with POE applications are high water pressure and environmental stress cracking of the plastic sumps (filter housings).

Did you know – Some sump manufacturer’s recommend replacement of clear sumps every five years and opaque sumps every ten years? 

If you are not sure how old a sump is, try looking on the bottom during the next routine cleaning and media change.  There is often a circular stamping in the plastic which indicate when the item was manufactured.  While the sump is out for cleaning, be sure to use a strong light source and examine the housing, especially the interior and around threads, for cracking.  And remember, clean and re-install in accordance with the manufacture’s recommendations, harsh chemicals and/or over tightening will almost certainly lead to accelerated degradation of the plastic. POU systems perform a similar function, however water is typically conditioned for only a single source/tap.  POU systems which use disposable all-in-one cartridges (think refrigerator water filters) help to reduce or eliminate sump failures; however, the head units may be damaged by over tightening or physical contact during installation.  Other modes of failure include filters which are not routinely changed and experience degradation of the plastic body and/or of the rubber seals (O-rings), and flexible supply lines which may become physically damaged or chemically embrittled.  Always label the water filter in accordance with the manufacturer’s recommendation using the installation date or the end-of-life date, so it is clear when it is time to change it!

3. Storage Tank Water Heaters

Depleted Anode Rod that no longer provides protection against corrosion
Depleted Anode Rod that no longer provides protection against corrosion

Perhaps some of the most common water loss events in homes relates to storage tank water heaters. Various industries have worked in recent years to inform the public that water heaters greater than ten years old should be considered for replacement. However, regular maintenance is required to lengthen the service life of the water heater to help achieve the recommended replacement interval. One of the most overlooked maintenance tasks to reduce internal tank corrosion and subsequent failure is inspection and replacement of the anode rod.

Did you know – Most manufacturers of storage tank water heaters recommend at least an annual inspection of the anode rod?

The anode rod provides sacrificial corrosion protection for the storage tank. Once the anode rod is depleted beyond a specified amount, it no longer offers sufficient corrosion protection and accelerated corrosion and failure of the tank occurs. While the anode rod is being inspected, be sure to perform the recommended flush of the tank and inspect the supply lines and connections to the home’s plumbing system.

Anode rods in good condition provide sacrificial corrosion protection in water heaters
Anode rods in good condition provide sacrificial corrosion protection in water heaters


4. Thermal Expansion Tanks


Often associated with water heaters and boilers, thermal expansion tanks are designed to protect a plumbing system from over-pressurization as a result of water volume expansion caused by the heating process. Expansion tanks are typically designed with an internal air chamber and an internal water chamber which are separated by a “rubber” bladder. As the heated water volume increase, the water presses on the bladder and expands into the air space to relieve the excess water pressure in the plumbing system. If an expansion tank fails internally, it may become water-solid and there is no longer an airspace for water expansion. This condition could cause plumbing system pressures to exceed the pressure rating of installed components (water filters, supply lines, etc.) and cause downstream failures.

Did you know – Most common expansion tanks use a Schrader-style air valve to inspect and change the air pressure inside the tank, just like on a car or bike tire?

If there is water coming out the air valve, or there is less than 20 pounds per square inch (psi) in a water heater expansion tank (or less than 10 psi in a boiler expansion tank), it is likely time to have it serviced or replaced. Alternately, inspect for excess pressure in the system using a water pressure gauge. Open a hot water tap and use a sufficient amount of hot water to cause the water heater to activate (turn on), then connect a water pressure gauge to an open, outside spigot. As the water heater heats, if the pressure on the gauge increases above 80 psi, it is time to have the system inspected and serviced.

5. Pressure Reducing Valves


These are critical and often unrecognized components in most residential plumbing system connected to a municipal water supply. Municipal water supplies often use high-pressure in the water main to “push” water for long distances throughout the town. A pressure reducing valve (PRV) is used between the municipal water supply and the household plumbing system to reduce incoming water pressure to a safe and constant level. Over time, PRV’s can become clogged with dirt and debris from the mainline or can experience internal degradation of diaphragms and seals due to attack from chemicals in the water supply. Connect a water pressure gauge to an open, outside spigot, during non-freezing weather, and allow it to dwell under pressure for several hours, or overnight, when water is not being used in the home. If the water pressure exceeds 80 psi, it is time to have the system inspected and serviced.

Did you know – Many PRV’s are designed to be cleaned and rebuilt in-place?

Maintenance of these valves requires shutoff of the main supply line, often at the street, and access to the device may be restricted; valves can be located in the home or at the street. If it has been more than five years since the PRV has been installed, inspected, or serviced, or pressure in excess of 80 psi has been observed, the PRV might need serviced or replaced.



If you find yourself spending a little more time around the house these days, take time to consider water loss prevention.  Knowing the average service life of commonly failed plumbing components and taking the time to perform some routine inspections and maintenance may prevent damage to personal belongings and save on costly repairs in the future.  Most components have service information available through the manufacturer’s website which will help you with inspection and planning activities to aid in water loss prevention.  Finally, don’t hesitate to schedule an appointment with a local pro if you have any questions, concerns, or need assistance with an inspection and tune-up of your home’s plumbing system!