Toilet Tank Components and Chlorides

By: John M. Holiday, P.E., Master Plumber

The Donan Component Testing Laboratory (CTL) studies numerous toilet tank components monthly.  Such components include toilet fill valves, ballcocks, and flush valve assemblies, as well as complete toilets and toilet tanks.

These toilet tank components are typically constructed of thermoplastic materials.  Thermoplastics widely used in toilet tank components include acetal (AC), polyester, polypropylene (PP), and acrylonitrile butadiene styrene (ABS).

Toilet fill valves contain a float assembly that actuates the flow of water to the toilet tank through a rubber diaphragm assembly at the top of the valve.  Fill valves typically contain adjustable mechanisms to conform to the height requirements of various toilet tanks.

Close-up fracture surface. Note discoloration and microfractures.

Photo 1: Close-up fracture surface. Note discoloration and microfractures.

A common failure mode for toilet fill valves is degradation and fracture due to contact with the toilet tank water.  The effects of chlorine on toilet fill valves are well known and documented (Photographs 1 and 2).  The plastic surfaces of the fill valves will discolor and fracture due to chlorides in the water.  Chlorides (chlorine or chloramines) are used by municipal water department as a disinfectant.  Chlorination has the benefit of reducing the risk of pathogenic disease in domestic water that may be used for drinking.  Pathogens including cholera, typhoid fever, and dysentery killed countless people prior to chlorination

of domestic water.  Because of the wide use of chlorine-containing compounds in domestic water, it is a foreseeable operating condition for plastic components intended to be used in toilet tanks.  The type of plastic used in the manufacture of fill valves varies, but the material that is most susceptible to degradation is acetal.

Typical fill valve failure due to exposure to toilet tank water

Photo 2: Typical fill valve failure due to exposure to toilet tank water

In 1974, congress passed the Safe Drinking Water Act, which provides the Environmental Protection Agency (EPA) with non-enforceable health guidelines for maximum residual disinfectant level goals (MRDLG) in drinking water.[1]  The guidelines specify a maximum chlorine or chloramine level of 4 milligrams per liter (mg/L) or 4 parts per million (ppm).

Chloramine is a water additive used to control microbes, particularly as a residual disinfectant in distribution system pipes.  It is formed when ammonia is added to water containing free chlorine.  Monochloramine is one form of chloramines commonly used for disinfection by municipal water systems.

Chlorinated water accelerates acetal degradation, even at low concentrations consistent with disinfectant usage in domestic water.[2]

Chlorides in conjunction with imposed stresses accelerate the degradation even more.  Imposed stresses include water pressure and mechanical stress from assembly or the manufacturing process.  In-house test results from one of the manufacturers of acetal found chlorine attack and deterioration due to exposures as low as 0.5 ppm.[3]

Readily available toilet tank products containing chlorides.

Photo 3: Readily available toilet tank products containing chlorides.

Chlorine is found in many cleaning products designed to be dropped in the toilet tank (Photographs 3 and 4).  These products are referred to

as automatic toilet bowl cleaner and are available wherever home cleaning products are sold.  The instructions for these chlorine-containing

tablets specify that the proper way to use the product is to place it inside the toilet tank.  The tablets then dissolve over the course of several weeks, thereby introducing chlorine-rich water into the toilet bowl after every flush.

The instructions provided with toilet fill valves usually provide a warning not to use bleach or chlorine cleaners in the toilet tank.  One of the problems with this type of manufacturer warning is that the information does not get to the owner/user of the toilet.

Photo 4: Typical instructions specify the use of cleaning tablets in the toilet tank.

Photo 4: Typical instructions specify the use of cleaning tablets in the toilet tank.

Toilet fill valves are typically installed by  a plumber, and the instructions and warning are not made available to the homeowner.  Regardless of whether the instructions were provided to the homeowner, there are design changes the manufacture could make to safeguard against the failure.

Since chlorine is used as a disinfectant in the potable water supply and chlorine-based in-tank products are readily available to the user, exposure to levels of chlorine above 0.5 ppm is a foreseeable operating condition.  Products designed to be installed in toilet tanks must be suitable for the expected operating conditions, and that includes exposure to water containing chlorine.

Typical new fill valve

Photo 5: Typical new fill valve

Toilet fill valves constructed of acetal plastic have the highest failure rate, based on evidence received at the Donan laboratory.  Fill valves constructed of other plastics have been less susceptible to failure.  One fill valve manufacturer has changed from acetal to polyester plastic, and this has resulted in fewer such failed components received in the lab.  The newer black (polyester) plastic shanks have been more resistant to chlorides than the older ones constructed of gray (acetal) plastic (Photographs 5 and 6).  The use of acetal in a plumbing application where chlorine will be present is a design defect due to use of a deficient material.  Although acetal is a versatile plastic material, it is known to be susceptible to degradation and failure when exposed to chlorinated water.

Acetal fitting failure in conjunction with polybutylene tubing resulted in a national class action lawsuit known as Cox vs Shell in 1995.  Acetal has found its way into plumbing supply lines, stop valves, and fill valves in the 1990s and have been failing ever since.

Thermoplastic inlet shank

Thermoplastic inlet shank

Donan CTL can study your toilet tank components for causation of a water loss.  If possible, it is always good to take photographs before removing the failed component.  If removing the specific component is not practical, the entire toilet or toilet tank can be shipped to Donan for study.  Not all toilet tank components contain date markings, so it is a good idea to ask the homeowner when the toilet was installed, as well as when any service work was performed.  Questions regarding the use of toilet tank cleaning products and municipal water are also useful in presenting a solid claim for subrogation.


[2] Failure of Plastics and Rubber Products by David Wright, Rapra Technology Limited 2001.

[3] Forensic Polymer Engineering, Lewis and Gagg, CRC Press, 2010.