Traditionally most homes used copper pipe to circulate hot and cold water. Since the 1970’s plastic pipes have increasingly replaced the traditional copper or galvanised steel pipes.
The last ten years have seen pipe-in-pipe systems commonly used 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 has 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 an unwanted taste and odour to drinking water. It has also been suggested that some of these substances may be carcinogenic.
There have been a number of investigations all over the world on the health issues and most are non conclusive or positive. A new study has just been released by the Norwegian Institute of Public Health on whether leaching or leakage products from these pipes are harmful to 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, as well as any susbsequent 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 of the PEX types still had an unpleasant smell and taste after a year
- The level of volatile organic compounds that leaked from new PEX pipes was generally low
- The level was further reduced with use
- No correlation was found between manufacturing methods and leaking products
This study was undertaken on a far more scientific basis than many tests or studies in Australia. It is not uncommon in Australia for international products that have undergone extensive testing to fail AS4020 based on an extremely subjective taste test from a panel of 5 – 7 people. In the Norwegian study 10 different types of PEX pipes were tested 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 method and leakage products. Two of the most commonly occurring substances detected in the water in the experiments were 2.4-di-tert-butyl-phenol and methyl-tert-butyl ether (MTBE). For three types of new pipe, MTBE was detected in higher concentrations than the US government’s recommended limits for taste and odour of drinking water (USEPA), but the values were reduced to below this limit after the tubes had been in use for a while.
This study confirms what the plumbing technicians at Whywait Plumbing frequently observe that no matter what the type of pipe there can be a taste or odour in new piping systems or where a house has been unoccuppied for a period of time. The taste and odour soon disappear once the water is in use in the house and is in constant circulation.