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PLUMBING SYSTEMS


n Copper pipe – copper is the most commonly used material for internal plumbing of domestic hot and cold water service pipes, and has sometimes been used in the past as the material for water mains. Like all metal pipes, copper is prone to corrosion and wear and tear. Copper has a high mechanical strength, and is cost-effective. Copper pipes are highly corrosion resistant to potable water. In some areas where the water is particularly ‘soft’, i.e. may be acidic or neutral pH 7, new installations of copper tubing may experience staining of sanitary fittings due to copper being picked up, resulting in a slightly metallic content within the water. This phenomenon is known as ‘blue water’ – more of this later. The issue here is that the internal protective film of patina Copper Oxide (CuO) or Cupric Oxide (Cu2


O) has not built up on


the inside of the pipework. If the problem persists, advice should be sought to resolve this problem.


High resistance to corrosion Copper is an excellent material to contain potable water, because generally it is highly resistant to corrosion to the environment, and does not generally interact with the different constituents of water transported, unlike iron, for example, which reacts with water to form iron oxide (rust). If iron pipes are used to carry water, they have to be coated in zinc, for example, to prevent corrosion. In some parts of the UK, and particularly in soft water areas, austenitic stainless steel pipes are used to carry water within buildings. However, in many situations copper pipes are preferred because they are easy to work with due to the ease with which they can be soldered together using a simple blowtorch or using copper press fittings, a flameless alternative to soldering copper pipe connections. In this system, a hydraulic tool is used to press specially designed connectors to join traditional pipes.


Copper pipe corrosion – issues with dissolved solder In rare situations, solder which has been used to join copper pipes containing drinking water starts to dissolve. If solder has been dissolved in water, it leaves a grey/silver sludge in sinks and baths. There are approved methods for soldering published by The Water Regulations Advisory Scheme, WRAS, and if the method is followed the jointing will be considered to be carried out in a ‘workmanlike manner’, and will comply with the Regulations and Byelaws. The requirements are the same for England, and for Wales, where they are called the Water Supply (Water Fittings) Regulations 1999, and in Scotland, the Scottish Water Byelaws 2004. The WRAS leaflet, ‘Solders and fluxes’, sets out the methods approved by your local water supplier for soldering (see www.tinyurl.com/yt6forqf).


Lead banned in solder


Previously, when lead was used extensively in solder, the contaminant in the water would be dissolved lead. Due to the


aforementioned health issues regarding ingestion of lead, this constituent of solder was, however, banned in the UK in 1986. Now, copper pipe solder includes a mixture of tin, copper, silver, zinc, and antimony. These metals in solution are not good for human consumption. The regional water supply companies are obliged by the EU Drinking Water Directive to provide wholesome water, and they use the following upper levels of these metals in drinking water: n Tin – not set in UK. n Copper – 2 mg Cu/litre. n Silver – not set in UK. n Zinc – not set in UK. n Antimony – 5 μg Sb/litre. n Lead - 0.01 mg Pb/litre.


Cuprosolvency and ‘blue water’ Problems relating to corrosion of copper and copper alloys in plumbing systems occur when the protective copper oxide layers either do not properly form in the first place, or become disrupted during service. This can potentially be due to a combination of circumstances occurring during installation, commissioning, and


Solder debris in a domestic sink.


Left: ‘Blue water’ in a domestic sink. Cuprosolvency describes a high general corrosion rate of copper, with the release of elevated dissolved copper ions in water, and the term ‘blue water’ describes discolouration of the water often seen against a white background, as found in sanitary fittings. Right: Discoloured water due to dissolved solder in the pipework.


38 Health Estate Journal July 2021


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