They are made of polymer and thermoplastic. Stabilisers prevent degradation and they need to be of a durable material. Since they are buried they are expected to be of amazing quality with expected life under pressure up to 100 years as well. It depends on the type of water and thermoplastic used.
They belong to flexible designed pipes, they require an advantage over the traditional pipes. The soil concretes down and stressed thr crown of the pipe and they do now break. The soil supports the stresses and the pipes can be easily compacted when they are flexible.
Chlorine can cause a major effect on its taste and odour however the levels of chlorine used do not affect the pvc piping at any cost. The use is 0.1mg of the total.
PVC-U, PVC-O and C-PVC pipe systems are completely safe for drinking water.
In Europe, the safety of PVC-U, PVC-O and C-PVC pipe systems for the transportation of drinking water is currently regulated and assessed nationally, although significant effort is ongoing at European level for the harmonisation of regulations and test methods. Regulations are presently determined by national bodies and third party certification is carried out by accredited laboratories and institutes who subsequently also carry out regular audits to ensure continued compliance.
As part of the harmonisation activities, European (EN) standards are under development for a number of test methods designed to assess the suitability of plastics pipe systems for drinking water. These standards include tests for organoleptic assessment (odour and flavour), the migration & leaching of substances into the water and microbial growth.
Migration: Different methods are used to detect the migration of substances present in PVC-U, PVC-O and C-PVC formulations. Leaching behaviour is assessed by prolonged direct contact of the potable water with the products in very severe conditions. Then the "migration water" is checked using different techniques, including searches for traces of molecules below the level of a few µg/l. Virtually nothing leaches out: the leachates are very similar to the blanks used when analysing them with techniques such as gas chromatography combined with mass spectroscopy (GC-MS).
Lead is not used anymore in stabilisers and such stabilisers have never been a source of lead in drinking water, as the stabilisers are immobilised within the PVC pipe structure during the manufacturing process. New stabiliser systems being used as alternatives to lead are fully assessed ("positive listing") and do not affect the drinking water characteristics in any way.
Traces of vinyl chloride monomer, sometimes exceeding regulatory limit of 0.5 µg of VCM/l of water, have been detected in some cases. It is important to keep in mind that this 0.5 µg/l limit is based on a guideline from the World Health Organisation (WHO) where the value has been set in order to guarantee an acceptable health risk, even in case of exposure during an entire lifetime.
These cases are related to exceptional circumstances (small diameter pipes in thinly populated regions, hence with intermittent flow). Most importantly, these cases appeared only in pipes installed before the 1970s, when the health risks of VCM were identified. PVC resin produced before then, although meeting all standards applicable at that time, contained higher levels of residual monomer than presently. Under usual conditions of use, water transported in PVC pipes produced in those days does also comply today with the current drinking water regulation. However, model calculations show that in exceptional circumstances (small diameter pipes, infrequent use) the VCM level reached after a period without flow can exceed the limit. No measurement result above the limit has ever been found in water flowing in pipes made from PVC produced after 1980.
It is important to stress that no vinyl chloride monomer is produced by the degradation or incineration of PVC products.
In any case, VCM concentration can easily be reduced to below the WHO guidance limit by flushing the pipe or by boiling the water. The high volatility of VCM leads to a rapid transfer from water into the atmosphere, where VCM does degrade by reaction with photochemically produced substances naturally present in the atmosphere. This limits its half-life of VCM in the atmosphere to between a few hours and a few days. VCM is therefore not persistent in the environment.
Microbial growth: PVC-U, PVC-O and PVC-C pipes are known to perform very well indeed according to the different methods used in Europe for the assessment of microbial growth of products in contact with drinking water (Germany, United Kingdom and The Netherlands). Many field studies confirm this good behaviour, which is linked to the absence of migration and the very good surface properties of these piping systems.
Odour & Flavour: Owing to absence of migration and low bacterial growth in PVC-U, PVC-O & PVC-C, the organoleptic properties of pipes made from these materials are generally very good, which is confirmed by regular testing by different European institutes.
As part of the EU harmonisation process, EN standards include EN 1420 & EN 1622 for the assessment of organoleptic properties and water quality; CEN-TR 16364 for the prediction of migration using mathematical modelling; EN 16421 for assessing microbial growth and EN15768 for the GC-MS identification of water leachable organic substances. In addition, EN 14395-1 is used for organoleptic assessment of water in storage systems.
Apart from these standardisation initiatives, a European positive list for substances used in plastics materials in contact with drinking water is also under development. This harmonised EU positive list will eventually replace several existing national drinking water positive lists. Further guidance can be found in ISO TR 10358.
