This study provides an interesting picture of HAA levels in distribution water in Scotland. HAAs concentrations from 298 Scottish water distribution zones were measured. The results obtained show that the median concentrations of HAA5 is 11.5 μg/L. In 0.7% of the zones under study, the average HAA5 concentration exceeds 60 μg/L. These zones are supplied by small WTWs (<3,300 people) and are using chlorination. The dominant species were trichloroacetic acid and dichloroacetic acid. Low HAA5 levels were observed in the groundwater systems and higher levels were observed in the surface water systems (median 12.4 μg/L). The chloraminated waters have lower HAA5 levels compared to chlorinated waters, but the difference is not that pronounced. The concentrations of HAA5 were higher in summer and autumn and lower in winter and spring but the difference was not statistically significant. The spatial variability of HAAs and THMs concentrations in two distribution zones using different disinfection strategies (chloramination and chlorination) was also studied. In both systems HAAs increased and decreased, a phenomenon likely related to biodegradation. There is also evidence that abiotic reduction of HAAs is possible for the chlorinated zone. Using flow cytometry we observed generally higher levels of total and intact cells in the chloraminated zone. Thus large numbers of dead cells can contribute to HAAs formation.