A group of Dutch researchers has completed a study on the plumbing between the water meter and consumer’s taps to determine whether stagnation and temperature may affect water quality.
“Our conclusion was that the microbial quality of drinking water changes during the overnight stagnation, and that change appears to be driven by the temperature of fresh water (coming from water mains),” said Ljiljana Zlatanović, lead author of the study.
The research was conducted using an experimental plumbing rig that simulated a two-storey house with two sets of stagnation experiments—during winter and summer months—with various stagnation intervals (up to 168 hours of stagnation). Water and biofilms were sampled at two different taps in the drinking water: a kitchen and a shower tap. Zlatanović explained that the results of the study were somewhat surprising.
“The main conclusion of previous research was that the overnight stagnation of water in domestic drinking water systems promotes the microbial growth in stagnant water. […] Even though nothing should be a surprise while conducting an experimental research, at the moment when we started getting the results that were different than those reported in previous studies, yes, we were kind of surprised,” she said.
The research contradicts the previously drawn conclusions about the microbial quality of drinking water is not applicable if the temperature of freshwater is higher than a certain threshold; for example, during the summer months.
The study stated, “Biofilm formed in the shower pipe contained more total and intact cells than the kitchen pipe biofilm. Alphaproteobacteriawere found to dominate in the shower biofilm (78 per cent of all Proteobacteria), while in the kitchen tap biofilm Alphaproteobacteria, Betaproteobacteria and Gammaproteobacteria were evenly distributed.”
The authors noted that the Netherlands is one of the few countries where drinking water is distributed without a residual disinfectant. In the Netherlands, the prevention of microbial growth in drinking water distribution systems is accomplished by the production of biologically stable water with low concentrations of assimilable organic carbon.
“Water companies in the Netherlands advise to flush domestic drinking water systems, but only after a long period of stagnation (more than 7 days). This advice seems to be based on an intuitive approach rather than on scientific facts, as only limited research has been carried out in the past years on the effect of stagnation in domestic drinking water systems. […] More research is needed on stagnation effects in domestic drinking water systems which would, among others, contribute to the knowledge on the required frequency of domestic drinking water system flushing. Moreover, with these new insights, very strict rules in installation design may be a bit loosened, opening new possibilities for applications of innovative technologies,” said Zlatanović.
The study entitled, “An experimental study on the influence of water stagnation and temperature change on water quality in a full-scale domestic drinking water system,” the Dutch study was published by Drs. Lj.Zlatanovića, J.P.van der Hoekab, and J.H.G.Vreeburgcd in the journal of Water Research, volume 123, 15 October 2017, pp 761-772, and is available online.