AbstractThe common existence of pressure transients in operational water distribution systems (WDS) requires their characterisation and assessment of their impact. This paper performs such characterisation by evidencing the occurrence and the differences in pressure transient behaviour in complex WDS. Ten samples of continuously recorded high resolution pressures from diverse networks and sources were analysed. The presented pressure traces show regular and occasional pressure transient waves in various complex networks. Histogram analysis of the rate of change of head provides some insight into transient behaviour in these sites. Although there was no distinct correlation between network characteristics (ie. length, diameter, age) and transient behaviour, network complexity was observed to change the transient characteristics. Transient characteristics were observed to be strongly influenced by likely sources, in particular commercial customers. The data highlights the need to understand, quantify and characterise transients and hence link to possible impacts, such as structural or water quality failures.