Significance and Assessment of the Biological Stability of Drinking Water

Abstract

Biologically-stable drinking water does not support the multiplication of micro-organisms in drinking water distribution systems. Such multiplication (regrowth) adversely affects water quality, e.g. by the presence of opportunistic pathogens, coliforms, increased heterotrophic colony counts, development of invertebrates. Disinfection is not effective against biofilms and sediments, which play a key role in regrowth, and cleaning methods are labor intensive. Regrowth therefore should be prevented by strictly limiting the concentration of compounds serving as energy sources for microorganisms. Growth measurements with selected pure bacterial cultures are used for assessing the concentration of easily assimilable organic carbon (AOC) in drinking water. Regrowth of heterotrophic bacteria is very limited in water supplies in the Netherlands at AOC concentrations below 10 μg of acetate-C equivalents per liter. The concentration of biodegradable organic carbon (BDOC), which is assessed as the reduction in DOC concentration in samples incubated with an assemblage of bacteria, did not decrease below the level of 0.2 mg/I in drinking water during distribution in Paris. Biological filtration processes are needed to remove the concentration of growth promoting compounds for obtaining biostable drinking water.