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Traditionally most homes used copper pipes to circulate hot and cold water. Since the 1970’s plastic pipes have increasingly replaced traditional copper or galvanised steel pipes.

Over the last ten years, pipe-in-pipe systems have been commonly installed to circulate water in most newly constructed homes. The inner pipe for drinking water is made of a plastic called cross-linked polyethylene (PEX).

Since the advent of plastic plumbing systems, there have always been questions regarding the effects on health and do they affect the taste and odour of drinking water. International studies have shown that plastic pipes can release substances that give drinking water an unwanted taste and odour. It has also been suggested that some of these substances may be carcinogenic.

Several investigations worldwide on health issues have been conducted, and most are inconclusive or positive. The Norwegian Institute of Public Health has just released a new study on whether leaching or leakage products from these pipes harm health and if they affect the taste and odour of drinking water. The potential leakage products consist of residues of additives used during manufacture to give plastic pipes their desired properties and any subsequent breakdown products.

The Norwegian study results indicated:

  • There are no health risks associated with drinking water from PEX pipes
  • A few types of PEX-pipe may cause prolonged undesirable taste and odour if the water remains in pipes over time
  • Although the taste and odour usually dissipate with use, water from two PEX types still had an unpleasant smell and taste after a year.
  • The volatile organic compounds that leaked from new PEX pipes were generally low.
  • The level was further reduced with the use.
  • No correlation was found between manufacturing methods and leaking products.

This study was undertaken far more scientifically than many tests or studies in Australia. It is common in Australia for international products that have undergone extensive testing to fail AS4020 based on a highly subjective taste test from a panel of 5 – 7 people. The Norwegian study tested ten different PEX pipe types for leaching products in a standardised laboratory test. The water was in contact with the tubes for 72 hours.

Three different manufacturing methods produce pipes known as PEX-a, PEX-b or PEX-c. These methods use slightly different additives, but this study found no correlation between production methods and leakage products. Two of the most commonly occurring substances detected in the experiment’s water were 2.4-di-tert-butyl-phenol and methyl-tert-butyl ether (MTBE). For three new pipe types, MTBE was detected in higher concentrations than the US government’s recommended limits for the taste and odour of drinking water (USEPA). Still, the values were reduced to below this limit after the tubes were used for a while.

This study confirms what the plumbing technicians at Whywait Plumbing frequently observe: no matter what type of pipe, there can be a taste or odour in new piping systems or where a house has been unoccupied. The taste and odour soon disappear once the water is in use in the house and is in constant circulation.

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