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The European Drinking Water Ordinance safety requirement has been valid since 1998. The guideline also sets out the legal responsibility of all parties involved in construction and operation.
An important aspect is to ensure the selection of correct materials and combinations for pipes, connectors and fittings for a new installation in accordance with the water condition.
Operating conditions that favor the growth of micro-organisms in the system can permanently cause more severe health hazards than the usual migration of materials during the initial weeks and months after commissioning.
This is especially the case with large distribution networks in hospitals, sports amenities, old people’s homes, hotels or apartment blocks housing several families. Due to long pipe sections and irregular water use, the risk of bacterial growth is especially high. The effect is greater when occupants are patients and older people whose immune system is weakened.
In many regions, permanent chemical disinfection is standard procedure for protecting water from bacterial infection. This is crucial in warmer regions where stagnation temperatures of above 25°C (77°F) are often unavoidable.
However, improved drinking water quality and tangible savings on maintenance and operating costs are available. This temperature guideline can be dispensed with if water quality at point of entry to the building – and specific rules for planning, construction and commissioning of the plant – are taken into consideration.
Tried and tested measures are presented here in a brief overview.
The danger of bacterial infection of the entire system is particularly high at constant temperatures between ~30°C and 50°C (~86°F and 122°F) if:
• Drinking water is stagnant for a long time in a pipe network and cold water is heated, for example, by adjacent heating pipework;
• Wastewater is fed into the pipe network due to a system fault, such as backflow.
For instance, Legionella pneumophila can cause legionnaire’s disease if steam is inhaled when showering. However, Pseudomonas aeroginosa (Illustration 2) are particularly feared in hospitals, as they can cause bed sores that are difficult to heal.
Taking regular samples from the pipe system – especially fittings that are rarely used – is the only way to determine whether the distribution network is largely free of germs (Illustration 3).
Chemical or thermal disinfection is a short-term solution for specific numbers of colonies, but generally the problem will be permanently treated only if the causes are identified and eradicated.
Future risks can be substantially reduced at the planning stage of a drinking water plant. By using needs-based pipework dimensions rather than reserves based, the required water exchange is favorably regulated in the piping network.
Exact manufacturer information should be incorporated in the calculation instead of standard values for individual resistance of press-connectors, valves or equipment.
Results for large-scale pipe networks often differ so substantially that total pipe widths can be one or two sizes smaller than calculated using recommended values (Illustration 4). Therefore, the entire water volume in the system is continually replaced quicker and the average cold-water temperature in the system is substantially reduced.
Microbial growth is thus reduced naturally.
Furthermore, regular water replacement in all parts of the plant is guaranteed if the consumer is involved in defining regular use – for example, hydraulically planning the WC tank at the end of a distribution pipe.
For the same reason, tapping points that are rarely used should be integrated into a series or closed circular piping system (Illustration 5). Branch lines should be exempt from this and should never contain more than 1L (2.1 US pints) of water.Continued...