In southern India, tens of thousands of village-level irrigation systems ('tanks' and feeder channels) are in disrepair. This paper analyses the results of a local NGO effort that focused on awareness-raising and advice to bring about self-sustained community action for irrigation system restoration. After designing a model structure that contains both motivational and capacity (social capital) factors, it is found that (pre-existing) collective social capital, as measured through five simple indicators, strongly correlates with success of the NGO strategy. The intensity of the NGO's effort shows a negative correlation with success, however. The discussion focuses on issues of social capital definition and measurement and the practical implications of the concept for environmental action, especially the difference between using existing social capital for environmental management versus the construction of social capital as a basis for later self-sustained environmental work.