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Drinking water hygiene in mobile water supply

Mobile and temporary water outlets in particular may harbour serious risks often hazardous to health, even if the installation appears to be properly maintained. This is because mobile systems as well as the entire public drinking water network may become contaminated through the unfortunate combination of various factors. In particular, these factors include reverse siphonage, reverse pressure and backflow of non-potable water into the drinking water installation. Due to the increased risk associated with mobile, temporary water outlets, compliance with measures for ensuring drinking water quality forms the highest priority. 

Mobile water outlets are used in various applications, including

  • land and water vehicles and aircraft (supply in coaches and on ships or the transfer of drinking water at airports)
  • backup supply (the water trucks of the German Armed Forces (Bundeswehr) or Technical Relief Service)
  • public fairs (refreshments and drinks supply), agriculture (irrigation systems) or
  • water supply on construction sites.

The determining factor is not whether the extracted water is used as drinking water, but rather whether the outlet point is connected with the drinking water installation.

Mobile and temporary water outlets in particular may harbour serious risks often hazardous to health, even if the installation appears to be properly maintained. This is because mobile systems as well as the entire public drinking water network may become contaminated through the unfortunate combination of various factors. In particular, these factors include reverse siphonage, reverse pressure and backflow of non-potable water into the drinking water installation. Due to the increased risk associated with mobile, temporary water outlets, compliance with measures for ensuring drinking water quality forms the highest priority

The requirements for water quality stipulated by the Drinking Water Ordinance must be adhered to throughout the water supply system. All components and parts that come into contact with drinking water must be made from suitable material that has no negative impact on the quality of the water. There are also strict standards regarding lead released by parts in contact with the drinking water. In 1998, upon publication of the EC Drinking Water Directive 98/83/EC, consideration was given to the problem concerning the release of certain alloy components into drinking water and the limit value sought by the WHO for lead in drinking water was set at 10 µg/l. After an amendment to the Drinking Water Directive in December 2013, installers in Germany must use materials that comply with these standards. 

In addition to components that are subject to strict standards regarding material and drinking water hygiene, operating conditions (assembly, use and disassembly) can also have an influence on the quality of drinking water. Mobile water supply systems in particular harbour increased health risks for the consumer as slight contaminations can occur in the system, and thus in the water. These can be caused by repeated assembly and disassembly of the installation at public events, for example, or in the water supply at construction sites. Temperature fluctuations, direct sunlight and the effects of vehicular traffic over supply lines also stress the pipes and can therefore represent risk factors as water contamination becomes a possibility. A human factor may also pose a considerable risk, particularly in the supply of mobile drinking water, in part because atypical hosing connections are often used. In such circumstances, it is important to avoid the risk of polluting the water supply system through contamination with non-potable water.

The areas of responsibility are meanwhile clearly defined by DIN 2001-2 and the DVGW Code of Practice W 408. Water suppliers are responsible for the quality of the water, from water extraction through to and including the central safety device at the point of delivery (supply section I). However, downstream from the point of delivery (e.g. beyond the stand pipe and as far as to the connected consumer), the organiser or operator bears the responsibility for the quality of drinking water within the distribution system (supply section II). Distribution systems are typically assembled for each event and then disassembled, stored or transported again after the event has finished. It is possible for contaminants to enter the distribution systems during this process. The operator of the subsequently connected system or consumers is also responsible for proper installation within their supply section (supply section III). These systems are often only operated on a seasonal or irregular basis and therefore have longer stagnation times than allowed for by the generally accepted rules of engineering for a central drinking water installation. 

Fundamentally, the requirements on water quality stipulated by the Drinking Water Ordinance must be adhered to for mobile water outlets. Stand pipes, connections and safety devices may only be installed by competent personnel. 

The use of suitable safety devices plays a central role in drinking water hygiene, particularly for mobile supply systems.

It is not always easy to categorise the water at the site of use. In practice, contaminated water of fluid categories 3 and 4 can often be encountered. At present, the safety combination frequently used in accordance with DIN EN 1717 (pipe aerators in combination with a backflow inhibitor) is therefore not able to cover every type of application. In order to safely prevent the backflow of substances up to category 4 into the drinking water installation, the BA backflow inhibitor (a ‘pipe isolator with adjustable medium pressure zone’ according to DIN EN 1717) is used as an approved safety valve.