The problem of arsenic-contaminated groundwater in Cambodia came to light relatively recently as compared with Bangladesh and surrounding areas, but 12 years on, not enough has been done in terms of awareness raising at the national level. Arsenic levels in some Cambodian well waters are comparable with those in some of the world's worst-impacted areas and awareness raising is a matter of urgency. This paper examines the impact of one awareness-raising initiative by a nongovernmental organisation (Resources Development International, RDI) by comparing knowledge levels in ‘mitigation’ and ‘comparison’ (control) villages. Socio-economic correlates of arsenic knowledge were analysed, and the effect of knowledge on water consumption behaviour was also explored. A structured questionnaire survey was undertaken in three villages with a total of 407 respondents. Findings suggest that in Cambodia, knowledge of the problem does not appear to be gendered, as has been reported in other countries, but wealth and education levels do impact upon knowledge where there have not been awareness-raising activities. As RDI focused their efforts on the most intensively affected area, it is difficult to separate out the effects of their awareness raising with ‘word of mouth’ and proximity to a high-risk area. The awareness-raising programme does appear, however, to have ironed out the effect of education and wealth on arsenic knowledge but may have bypassed the more elderly. Knowledge of the problem generates a greater change in water consumption behaviour than has been reported elsewhere. Overall, knowledge of the problem remains very low.