Using a tracer to identify water supply zones in a distribution network

This paper presents a methodology that can effectively identify contributions of water sources to end-use water consumption in distribution network locations. The sector selected for the study is a residential sector of Quebec City supplied with drinking water directly from the main supply pipes from the water treatment plant and by re-chlorinated water from a reservoir. The proposed methodology relies on three strategies: a hydraulic characterization of the distribution network, a tracer study and a water quality characterization study. A tracer study was conducted by injecting CaCl₂ brine at the reservoir outlet in order to increase calcium concentrations in water from that source. It was then possible to associate sampling points at which calcium concentrations showed an increase during the test as being supplied by the reservoir. A water quality characterization study was conducted simultaneously with the tracer study, making it possible to validate the distribution zones identified. This validation was made possible by analysing the difference between residual chlorine values from the two sources; in fact, water from the reservoir had distinctively higher levels due to re-chlorination. With this fact, it was possible to identify distribution zones at points where the calcium concentration had remained constant during the tracer test.