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Are HDPE pipes safe for drinking water?

Dec. 09, 2021

Are high-density polyethylene (HDPE) pipes a good environmental choice for potable water applications?


Cross-linked polyethylene (PEX) has been used in radiant heating systems since the 1980s and has become popular for potable water in recent years. PEX or PEX-lined piping has wide regulatory acceptance nationwide, but PEX requires special fittings and is not recyclable. The chemical cross-linking required to produce PEX adds cost and increases the potential for contaminants to migrate from the plastic into the water. For example, when PEX piping is used underground, the pipe may come into contact with groundwater.


During the California regulatory approval process, Reid (2005) provided testimony that the gasoline additive methyl tertiary butyl ether (MTBE) or pesticides may infiltrate PEX piping in areas where groundwater is contaminated with petroleum products.


The final EIS indicated that while chemical migration was a concern, contaminant levels would rapidly decline over time to safe levels. Opponents advocate more thorough testing of polymer formulations and chemical leaching solutions.


High-density polyethylene (HDPE) pipelines have been used in non-potable water applications for decades. In particular, HDPE piping is often the preferred choice for welded joints. While special equipment is required to form the welds, welding does not require separate fittings, a common source of leaks and contaminant infiltration. HDPE is very flexible and can withstand harsher field handling than more brittle polymers. Flexibility also allows turns in the piping system without the need for additional fittings.

Are HDPE pipes safe for drinking water?


For potable water, HDPE was initially limited to cold water service applications because early formulations were not strong enough to handle the high temperatures of hot water systems. Suppliers subsequently developed cross-linked polyethylene (PEX) with superior strength and high-temperature performance. EX is common in radiant floor heating applications and is increasingly used in domestic hot and cold water systems. However, as noted above in the original question, the available pipe sizes are too small for larger commercial installations. HDPE and PEX are both polyethylene (PE), but because of their different properties, care should be taken not to confuse these two very different materials.


HDPE can be used in hot water as a liner for multilayer piping where strength is provided by another piping layer, such as aluminum, but multilayer piping does not provide all the performance benefits of plastic alone.


Conclusions and Key Findings.


HDPE is widely accepted by standards organizations and regulatory bodies for potable cold water applications. High-temperature HDPE formulations have been widely used in Europe for some time, but only a few materials are ANSI/NSF certified for domestic hot water use in the United States.


Independent studies have shown that chemical contaminants do migrate from HDPE piping materials into water and can infiltrate some plastic pipes when in contact with contaminated soil. However, these studies are inconclusive as to the effects of these contaminants on human health.


Those who anticipate using HDPE, especially in hot water applications, should request data and certifications from their suppliers regarding chemical migration, taste and odor, and high temperature performance.


Those most concerned about chemical contamination may prefer to forgo the use of plastic altogether, but plastic piping offers significant advantages over copper in terms of installation, use, cost and the environment.

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