Proliferation of L. pneumophila in premise plumbing poses a public health threat. Extended water treatment using physicochemical and biofiltration processes, including slow sand filtration, at four surface water supplies in The Netherlands reduces the microbial growth potential of the treated water to a minimum level, and the distributed drinking water complies with high quality standards. However, heating of the water in warm tap water installations increases the concentration of easily assimilable organic compounds, thereby promoting biofilm formation and growth of L. pneumophila . Prevention of biofilm formation in plumbing systems by maintenance of a disinfectant residual during distribution and/or further natural organic matter (NOM) removal is not feasible in the supplies studied. Temperature management in combination with optimized hydraulics and material selection are therefore essential to prevent growth of L. pneumophila in premise plumbing systems. Still, reducing the concentration of biodegradable compounds in drinking water by appropriate water treatment is important for limiting the Legionella growth potential.

High drinking water temperatures occur due to climate change and could enhance the growth of opportunistic pathogens in drinking water systems. We investigated the influence of drinking water temperatures on the growth of Pseudomonas aeruginosa, Stenotrophomonas maltophilia, Mycobacterium kansasii and Aspergillus fumigatus in drinking water biofilms with an autochthonous microflora. Our results reveal that the growth of P. aeruginosa and S. maltophilia in the biofilm already occurred at 15.0 °C, whereas M. kansasii and A. fumigatus were able to grow when temperatures were above 20.0 °C and 25.0 °C, respectively. Moreover, the maximum growth yield of P. aeruginosa, M. kansasii and A. fumigatus increased with increasing temperatures up to 30 °C, whereas an effect of temperature on the yield of S. maltophilia could not be established. In contrast, the maximum ATP concentration of the biofilm decreased with increasing temperatures. We conclude from these results that high drinking water temperatures caused by, e.g., climate change can result in high numbers of P. aeruginosa, M. kansasii and A. fumigatus in drinking water systems, which poses a possible risk to public health. Consequently, it is recommended for countries with a more moderate climate to use or maintain a drinking water maximum standard temperature of 25 °C.

To guarantee a good water quality at the consumer’s tap, natural organic matter (NOM) should be (partly) removed during drinking water treatment. The objective of this research is to measure the effect of NOM removal by ion exchange on the biological stability of drinking water. Experiments were performed in two lanes of the pilot plant of Weesperkarspel in the Netherlands. The lanes consisted of ozonation, softening, biological activated carbon filtration and slow sand filtration. Ion exchange in fluidized form was used as pre-treatment in one lane and removed 50% of the dissolved organic carbon (DOC); the other lane was used as reference. Compared to the reference lane, the assimilable organic carbon (AOC) concentration of the finished water in the lane pretreated by ion exchange was 61% lower. The biofilm formation rate of the finished water was decreased with 70% to 2.0 pg ATP/cm2.day. The achieved concentration of AOC and the values of the biofilm formation rate with ion exchange pre-treatment showed that the biological stability of drinking water can be improved by extending a treatment plant with ion exchange, especially when ozonation is involved as disinfection and oxidation step.

Waternet, the water cycle company of Amsterdam and surroundings, manages three large diameter pre-stressed concrete pipelines (PCPs), which transport pre-treated water for drinking water production and industrial use. These pipelines pass through critical areas in the densely populated West of The Netherlands; in the centre and along the edge of a primary dyke along the Amsterdam-Rhine Canal, crossing several other dykes, along and across highways and railways and nearby the runway of Amsterdam Airport. Since a leaking pipeline caused the collapse of a dyke in the South of The Netherlands, the Security Council required the Dutch water supply utilities to improve their management of the pipelines near vital infrastructure. The goal of this study is to develop an integrated monitoring strategy for the pipelines, to ensure that the pipelines do not affect the functioning and stability of the vital infrastructure along the pipelines route. The main focus of the strategy is to prevent pipeline failure and to detect pipeline failure in an early stage (before it can cause harm). Failure mechanisms of PCPs were analyzed; leaking joints caused by ground movement were identified as the most likely failure mode. Based on the timescale of possible causes of failure a combination of currently applied and "innovative" monitoring techniques was selected for the monitoring strategy.