This paper presents the results of an ongoing investigation into the impact of routine operations such as pump cycling and leak repair on water quality in a specific Canadian distribution system. This research demonstrates occurrence of intrusion into the distribution system at full scale. To monitor the impact of pump operation, sampling protocols involving the use of high-speed pressure data and online particle counters in the distribution system have been developed. For the repair of pipe leaks, soil and water samples in the vicinity of the repaired main, combined with sampling of the distributed water at customer houses and at the flushed hydrants, have been conducted. Results indicate that hydraulic transients induced by pump start-ups and stoppages can sometimes induce a direct response in terms of particle counts. However, the effect is not observed systematically and the response behavior varies between distribution system locations. For the repair of pipe leaks, evidence of the intrusion of either soil or dirty water during the repair work was obtained on one occasion; specifically, an elevated concentration of aerobic sporeformers was measured in a water sample collected at the hydrant during the flushing operation. Includes 5 references, tables, figures.