Behavioural spillover, in which initial behaviour undertaken by individuals leads to other behaviours, has attracted attention of environmental policymakers. We propose to understand behavioural spillover of goal-setting using a goal theoretical perspective. Using a randomized controlled trial, this study examines and compares spillover effects – from electricity-saving to water-saving – of three types of goal-setting intervention. In a field experiment carried out in Singapore, 150 households were randomly assigned to the control group or one of three treatment groups – where they set electricity-saving goal by themselves (SG), were assigned a 10% goal (AG), or were assigned a 10% goal with a guarantee of a monetary reward for goal achievement (AGM). An electricity consumption reportwas also provided weekly to participants in the treatment groups during the six weeks of intervention; participants in the control group received no information. We found that all the three types of goal-setting intervention significantly reduced participants’ electricity consumption. Participants in the SG group recorded a positive spillover effect to water-saving; however, no spillover was found in the AG and AGM groups. Finally, limited evidence was found that shows that goal commitment can moderate the spillover effect. Hence, the self-set goal is preferred to promote positive spillover and these results reduce the concern that monetary incentive could trigger negative spillover.