PEX Tubing for Domestic Water Systems

By Susan Ecker

Rumsey Engineers, Inc.

Cross-linked polyethylene tubing (PEX) is an alternative material for domestic water systems piping systems. PEX tubing is becoming widely used for domestic water systems throughout the U.S. because it is easy to install, cost effective, reliable, flexible in design and corrosion resistant. PEX seems to be ideal for use in domestic water systems, however, in California, the use of PEX is no longer allowed by the California Plumbing Code (CPC) until an environmental review under the California Environmental Quality Act (CEQA) is performed.

In the 2001 edition of the CPC, PEX is listed as an acceptable material for domestic water piping. It was after the CPC was issued that the approval of PEX was rescinded. Certain jurisdictions within California may allow the use of PEX, but at this time, California Plumbing Code does not. The CPC is based on the Uniform Plumbing Code (which allows the use of PEX tubing for domestic water systems) with California modifications.

What is PEX?

According to the Plastics Pipe Institute, PEX is polyethylene that has been chemically or physically modified to cause the individual molecules to link together permanently. Once polyethylene is cross-linked, it becomes a thermo-set plastic, meaning that it cannot be melted and reshaped. The cross-linking process cannot be reversed. PEX has desirable high temperature strength, reduced sensitivity to notching, improved chemical resistance and good flexibility. PEX tubing is produced in nominal dimensions from 3/8 in. to 2 in., is available in natural (white) or colors and in coils or 20-ft. straight lengths. PEX is listed as an acceptable material in all national model plumbing codes including the International Plumbing Code, Uniform Plumbing Code, and the National Standard Plumbing Code. It is important to check with the local Building or Plumbing Official to determine if they are permitting the use of PEX.

Per the Plastics Pipe Institute, PEX is a good material for plumbing systems for the following reasons:

• High temperature capability, pressure rated up to 200 F
• High pressure capability/stability (reduced creep)
• Smooth wall, excellent flow characteristics
• Quiet operation
• Reduced heat loss and condensation
• Flexibility for design
• Proven long life, rigorous certifications, highly tested
• Corrosion resistance (not possible)
• No pinhole problems
• No build-up inside
• Flexibility, reduced fittings, faster installation
• Flexibility for design
• Secure, reliable fittings reduce leaks
• Lightweight, easy and safe to transport and handle
• Efficient to install, long coils reduces joints
• Clean, safe to work with

Other items to keep in mind about PEX piping installations include:

• PEX must not be stored or installed in areas where it will be exposed to sunlight, either direct or indirect. Many PEX materials have extended ultraviolet (UV) protection for exposure that occurs at the job site but none are rated for continuous exposure.
• Do not use fittings under slabs, unless protected (wrapped) or made of special materials.
• PEX is flexible so an installation looks different than an installation with rigid pipe.

PEX and the California Pipe Trades Council

Since 2001, when California first considered allowing the use of PEX, there has been ongoing litigation between California and the Plastic Pipe and Fittings Association (PPFA). The plumbers union was joined by environmental and consumer groups, including the Sierra Club, the Planning and Conservation League, Consumer Federation, Communities for a Better Environment, the Center for Environmental Health and the California Professional Firefighters Association in urging thorough environmental review of PEX.

The PPFA argued that California should be required to allow the use of PEX without an environmental review. When California decided to conduct environmental review, the PPFA sued California in Los Angeles Superior Court and obtained a trial court order requiring California to allow the use of PEX without an environmental review.

In 2004, after three years of litigation, the California Court of Appeal in Los Angeles ruled that PEX must go through an environmental review under the CEQA. There have been a number of studies and testing performed on PEX tubing. Of all of the studies and testing performed only one is truly independent. That testing was performed by the NSF and will be discussed in detail below. Studies funded by the plumber's union (United Association (UA) which represents the plumbing and pipe fitting industry with over 300,000 members across the United States and Canada) have shown that PEX pipes leach methyl tertiary butyl ether (MTBE) and benzene into drinking water, that PEX may prematurely decay and rupture, and that the flammable material may allow fires to spread rapidly through homes with PEX plumbing.

NSF/ANSI Standard 61

NSF International, a not-for-profit, non-governmental organization, provides standards development, product certification, education, and risk management for public health and safety. NSF focuses on food, water, indoor air, and the environment. NSF/ANSI Standard 61 is entitled Drinking Water System Components-Health Effects. This is the American National Standard for health effects of drinking water system components. It establishes the health effects requirements for the chemical contaminants and impurities that are indirectly imparted to drinking water from products, components and materials used in drinking water systems. The standard is maintained by a Joint Committee with equal representation from regulators (such as Environmental Protection Agency (EPA), Health Canada, and state drinking water officials), users (such as water purveyors, utilities, and engineers) and manufacturers. The NSF/ANSI Standard 61 is accredited by the American National Standards Institute, which ensures the standard is developed and maintained using an open, consensus process and has representation by all stakeholders.

Testing

According to NSF, first, a formulation review is performed on the material to determine what possible contaminants could leach out into drinking water and determines what type of chemical extraction testing is necessary. PEX tubing is tested by exposing the tubing to formulated exposure waters, and then analyzing the exposure waters for contaminants. Three separate formulated waters are used during the product exposure. A pH 5.0 and 10.0 exposure water are separately used for exposures as these waters are aggressive toward extraction of metallic contaminants. A pH 8.0 water is used during the exposure for organic based contaminants. The tubing samples containing water are heated to 140 F (60 C), for domestic hot water systems or 180 F (82 C) for commercial hot systems. Tubing is conditioned by exposure to the formulated waters for 14 days with water being changed on 10 of those days. The water collected from the final 16-hour exposure period is then analyzed for contaminants. Any contaminants found must be below EPA or Health Canada levels for regulated contaminants. For non-regulated contaminants found, NSF/ANSI Standard 61 sets health based pass/fail levels based on review of available toxicity data using the risk assessment procedures in annex A of the standard.

Analysis

According to NSF, water exposed to PEX tubing and associated fitting systems are tested for the following contaminants as required by NSF/ANSI Standard 61:

• Volatile Organic Compounds (VOCs)
• Semi-volatile compounds (base neutral acid scan by Gas Chromatography/Mass Spectroscopy)
• Phenolics
• Regulated Metals scan including antimony, arsenic, barium, beryllium, cadmium, chromium, copper, lead, mercury, selenium, and thallium
• Methanol
• Tertiary butyl alcohol
• Methyl tertiary butyl ether (MTBE)
• Any other potential contaminant identified during the formulation review.
• These test methods are capable of detecting contaminants in water as low as 4 parts per billion
  (4 ppb) and lower, equivalent to 0.0000004% concentration.

Marking

PEX tubing meeting the health effects requirements of NSF/ANSI Standard 61 will bear either the NSF-61 Mark or the NSF pw (potable water) Mark. The NSF pw Mark indicates the product meets the health requirements of NSF-61 as well as performance, long term strength and quality control requirements as required by NSF/ANSI Standard 14- Plastic Piping Components and Related Materials. If a product has only a NSF rfh mark, this indicates the product has only been evaluated for radiant floor heating applications.

Conclusion

When there are two opposing view points such as the manufacturers and the trade groups on one side and the plumber's union one the other, the only way to determine the truth is to obtain test results from an independent third party. It appears that NSF has a 60 year history of protecting public health and is a respected third party. NSF has tested PEX tubing and found it to be within the parameters set.

Also, before allowing PEX to be allowed in the model plumbing codes this independent testing was most likely considered. If this testing was inconclusive or insufficient most likely the model plumbing codes would not have allowed PEX to be an accepted material.

California should complete their independent review under CEQA and determine if PEX too much of a risk to allow in domestic water systems. Many trends that start in California are followed in other parts of the nation. The results of the environmental review may have an impact on plumbing codes nation wide either by affirming the stance that the model code bodies have taken or bringing new information to light that may change the way these code bodies view PEX piping for domestic water systems.

Susan R. Ecker is a senior plumbing engineer with Ramsey Engineers Inc. in Oakland, CA. She has extensive experience in designing plumbing systems for industrial and commercial market sectors. Ecker can be reached at secker@ramseyengineers.com.