Maintaining a Disinfectant Residual in the Distribution System

Abstract

To provide safe drinking water at the tap of a consumer, a disinfectant residual must be maintained in the system. The recognition that the residual declines with distance and time has required a new look at the distribution system. No longer is it satisfactory to have safe water at the treatment plant reservoir, but it must also be guaranteed throughout the system. Thus, over the past few years attention has been focused on the processes which take place in the system. First, it is well known that when the disinfectant residual becomes low, a regrowth of bacteria in the system takes place. This decline in the residual occurs when the disinfectant reacts with organic material in the bulk of the water and in reactions with the biofilm on the surface of the pipes. Two parameters influence this: one, the type and level of disinfectant, and two, the age of the water. There are operational interventions, and there are possibly structural interventions. These will be discussed in the following sections. But what is also needed is a timely determination of the bacterial level in the system-an early recognition of elevated bacterial counts allows a timely response.