For several millennia, humans have created built environments to harness natural processes for their benefit. Today, human-environment interactions are mediated extensively by physical infrastructure in both rural and urban environments. Yet studies of social-ecological systems (SESs) have not paid suficient attention to how infrastructure influences coupled natural and social processes. This misses an important point: critical infrastructure is often a public good that depends on cooperation of the agents who share it. Using a model of an irrigation system (the most ancient of public infrastructure systems) as a testing ground, we found that two properties of infrastructure, threshold of provision and asymmetric access to benefits, greatly influence SES sustainability. Asymmetric access to benefits induces regimes of economic inequality. High thresholds suppress economic inequality, but at the cost of increased likelihood of system collapse. Low thresholds help to avoid system collapse, but may make the system more vulnerable to economic inequality and socioeconomic stresses. Understanding how small scale irrigation SESs may respond to such globalization-related stresses is relevant for agricultural policy and our results provide some general guidance in this regard.