This paper describes the design and operation of a passive siphon sampler for the collection of event-based water quality data from a remote dryland river. The materials used to construct the siphon sampler were modified to better adapt the design for the collection of non-conservative water quality parameters and for use in high-intensity flow conditions typical of Australia's dryland rivers. The performance of the siphon sampler was evaluated in a pilot study of water metals in the rising-stage floodwaters of the upper Leichhardt River catchment, north-west Queensland, Australia. Field blanks were used to quantify the extent of contamination of the collected waters by sampling media, atmosphere exposure or water intrusion during an event-based collection period. The use of inert materials, such as high-density polyethylene plastic, and careful cleaning with 10% nitric acid washes prior to use reduced environmental contamination of the collected sample. Below detectable levels of Pb and Zn and minor concentrations of Cu (1.8 and 1.3 μg L–1) were reported in rinsate and atmospheric blanks that were exposed in the field for less than 24 h. Atmospheric and flood blanks that remained in the field for greater than 2 weeks and remained in the siphon samplers throughout the duration of the flood events reported quantifiable concentrations of metals. For the case of the upper Leichhardt River catchment, the siphon sampler met the need of providing event-based water collection data and offered a practical, low-cost alternative to conventional event-based sampling techniques. Copyright © 2011 John Wiley & Sons, Ltd.