Direct evidence of microbiological water quality changes on bacterial quantity and community caused by plumbing system.

Drinking water quality deteriorates from treatment plant to customer taps, especially in the plumbing system. There is no direct evidence about what the differences are contributed by plumbing system. This study compared the water quality in the water main and at customer tap by preparing a sampling tap on the water main. The biomass was quantified by adenosine triphosphate (ATP) and the microbial community was profiled by 454 pyrosequencing. The results showed that in distribution pipes, biofilm contributed >94% of the total biomass, while loose deposits showed little contribution (< 2%) because of the low amount of loose deposits. The distribution of biological stable water had minor effects on the microbiocidal water quality regarding both quantity (ATP 1 ng/L vs. 1.7 ng/L) and community of the bacteria. Whereas the plumbing system has significant contribution to the increase of active biomass (1.7 ng/L vs. 2.9 ng/L) and the changes of bacterial community. The relative abundance of Sphingomonas spp. at tap (22%) was higher than that at water main (2%), while the relative abundance of Pseudomonas spp. in tap water (15%) was lower than that in the water from street water main (29%). Though only one location was prepared and studied, the present study showed that the protocol of making sampling tap on water main offered directly evidences about the impacts of plumbing system on tap water quality, which makes it possible to distinguish and study the processes in distribution system and plumbing system separately.

Aeromonas species from non-chlorinated distribution systems and their competitive planktonic growth in drinking water.

Aeromonas is included in the Dutch Drinking Water Decree as an indicator for elevated microbial regrowth in non-chlorinated drinking water distribution systems (DWDS). The temporal and spatial diversity of Aeromonas species in ten DWDS and their planktonic growth characteristics for different carbon sources was investigated. Genotyping of the gyrB gene of isolates showed a non-systematic temporal and spatial variable prevalence of seven different Aeromonas species in these DWDS and no correlation with AOC-P17/NOX and Aeromonas concentrations. Pure cultures of these seven species showed a high affinity to low concentrations (µg/L) of individual amino acids and fatty acids, compounds associated with biomass. Growth occurred at 0.5 µg-C/L of an amino acid mixture. Growth of a mixed community of A. rivuli, A. salmonicida, A. sobria and A. veronii in drinking water occurred in pasteurized samples, however, no growth and decay occurred in competition with the autochthonous bacteria (non-pasteurized samples). This community also failed to grow in non-pasteurized distribution samples from a location with clear increase in planktonic Aeromonas concentrations in the transported drinking water. For competitive planktonic growth of Aeromonas an amino acid concentration of ≥5 µg-C/L is required. AOC-P17/NOX concentrations showed that such concentrations are not expected in Dutch drinking water. Therefore, we suspect that competitive planktonic growth is not the major cause of the observed non-compliance with the Aeromonas standard in non-chlorinated DWSD.Importance The occurrence of the bacterial genus Aeromonas in non-chlorinated drinking water in the Netherlands is regarded as an indication for elevated microbial regrowth in the distribution system. Identification of the prevalent species in ten distribution systems by genotyping yielded seven different species, with A. rivuli, A. veronii and A. sobria as the most dominant ones. Planktonic growth experiments of pure cultures confirmed former published affinity of Aeromonas for certain biomass compounds (amino and fatty acids). In competition with the autochthonous microflora, however, planktonic growth was not observed, only after addition of a threshold amino acid concentration of 5 µg-C/L. Based on our results and further observations we deduced that planktonic growth of Aeromonas in the DWDS is not very likely. Benthic growth in loose deposits and planktonic release is a more plausible explanation for the observed planktonic increase of Aeromonas.

Primary Colonizing Betaproteobacteriales Play a Key Role in the Growth of Legionella pneumophila in Biofilms on Surfaces Exposed to Drinking Water Treated by Slow Sand Filtration.

Slow sand filtration with extensive pretreatment reduces the microbial growth potential of drinking water to a minimum level at four surface water supplies in The Netherlands. The potential of these slow sand filtrates (SSFs) to promote microbial growth in warm tap water installations was assessed by measuring biofilm formation and growth of Legionella bacteria on glass and chlorinated polyvinylchloride (CPVC) surfaces exposed to SSFs at 37 ± 2°C in a model system for up to six months. The steady-state biofilm concentration ranged from 230 to 3,980 pg ATP cm-2 on glass and 1.4 (±0.3)-times-higher levels on CPVC. These concentrations correlated significantly with the assimilable organic carbon (AOC) concentrations of the warm water (8 to 24 µg acetate-C equivalents [ac-C eq] liter-1), which were raised about 2 times by mixing cold and heated (70°C) SSFs. All biofilms supported growth of Legionella pneumophila with maximum concentrations ranging from 6 × 102 to 1.5 × 105 CFU cm-2 Biofilms after ≤50 days of exposure were predominated by Betaproteobacteriales, mainly Piscinibacter, Caldimonas, Methyloversatilis, and an uncultured Rhodocyclaceae bacterium. These rapidly growing primary colonizers most likely served as prey for the host amoebae of L. pneumophilaAlphaproteobacteria, mostly Xanthobacteraceae, e.g., Bradyrhizobium, Pseudorhodoplanes, and other amoeba-resistant bacteria, accounted for 37.5% of the clones retrieved. A conceptual model based on a quadratic relationship between the L. pneumophila colony count and the biofilm concentration under steady-state conditions is used to explain the variations in the Legionella CFU pg-1 ATP ratios in the biofilms.IMPORTANCE 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.

Assessing the origin of bacteria in tap water and distribution system in an unchlorinated drinking water system by SourceTracker using microbial community fingerprints.

The general consensus is that the abundance of tap water bacteria is greatly influenced by water purification and distribution. Those bacteria that are released from biofilm in the distribution system are especially considered as the major potential risk for drinking water bio-safety. For the first time, this full-scale study has captured and identified the proportional contribution of the source water, treated water, and distribution system in shaping the tap water bacterial community based on their microbial community fingerprints using the Bayesian "SourceTracker" method. The bacterial community profiles and diversity analyses illustrated that the water purification process shaped the community of planktonic and suspended particle-associated bacteria in treated water. The bacterial communities associated with suspended particles, loose deposits, and biofilm were similar to each other, while the community of tap water planktonic bacteria varied across different locations in distribution system. The microbial source tracking results showed that there was not a detectable contribution of source water to bacterial community in the tap water and distribution system. The planktonic bacteria in the treated water was the major contributor to planktonic bacteria in the tap water (17.7-54.1%). The particle-associated bacterial community in the treated water seeded the bacterial community associated with loose deposits (24.9-32.7%) and biofilm (37.8-43.8%) in the distribution system. In return, the loose deposits and biofilm showed a significant influence on tap water planktonic and particle-associated bacteria, which were location dependent and influenced by hydraulic changes. This was revealed by the increased contribution of loose deposits to tap water planktonic bacteria (from 2.5% to 38.0%) and an increased contribution of biofilm to tap water particle-associated bacteria (from 5.9% to 19.7%) caused by possible hydraulic disturbance from proximal to distal regions. Therefore, our findings indicate that the tap water bacteria could possibly be managed by selecting and operating the purification process properly and cleaning the distribution system effectively.

Assessment of the microbial growth potential of slow sand filtrate with the biomass production potential test in comparison with the assimilable organic carbon method.

Slow sand filtration is the final treatment step at four surface-water supplies in the Netherlands. The microbial growth potential (MGP) of the finished water was measured with the assimilable organic carbon (AOC) method using pure cultures and the biomass production potential (BPP) test. In the BPP test, water samples were incubated untreated at 25 °C and the active-biomass concentration was measured by adenosine tri-phosphate (ATP) analysis. Addition of a river-water inoculum improved the test performance and characteristic growth and maintenance profiles of the water were obtained. The maximum ATP concentration attained within seven days and the cumulative biomass production after 14 days of incubation (BPC14, d ng ATP L-1) showed highly significant and strong linear relationships with the AOC in the slow sand filtrates. The lowest AOC and BPC14 levels were observed in the supplies applying dune filtration without ozonation in post treatment, with AOC/TOC = 1.7 ± 0.3 µg acetate-C equivalents mg-1 C and BPC14/TOC = 16.3 ± 2.2 d ng ATP mg-1 C, corresponding with 1.2 ± 0.19 ng ATP mg-1 C. These characteristics may represent the lowest specific MGP of natural organic matter achievable by biofiltration at temperatures ≤20 °C. The AOC and BPC14 concentrations in the slow sand filtrate of the supply treating lake water by ozonation with granular-activated-carbon filtration and slow sand filtration as post treatment increased with decreasing temperature. The BPP test revealed that this slow sand filtrate sampled at 2 °C contained growth-promoting compounds that were not detected with the AOC test. These observations demonstrate the utility of the BPP test for assessing the MGP of drinking water and show the performance limits of biofiltration for MGP reduction.