So the result is that you don t see any coliforms, but you didn t kill the viruses or protozoa coming into the distribution system. You think the situation is safe, but your indicator concept doesn t work properly. You say we should produce biologically stable water. It sends you into a devil s circle, with the dog biting its own tail. You produce more and more AOC, and you have to carry a higher and higher residual.
Nobody here questions the advantage of chlorine.
Abel Wolfman advanced the science of chlorine as a disinfectant, but it is a different story to carry high concentrations of chlorine in the distribution system with long retention times and produce two times more trihalomethanes than you produced in the first place. Obviously, the most effective and desirable way to prevent recontamination is to install pathogen-free storage and distribution equipment initially and to prevent its subsequent recontamination by proper maintenance. If it is not possible to adhere to the conditions for pathogen-free storage and distribution listed above, then a chlorine residual may protect the water under certain conditions but not others. There are many potential scenarios in which the presence of a residual may serve to foster a false sense of security that encourages negligence and endangers people s health. This can be illustrated with the following examples.