A common paradigm in studies of human cooperation is that individuals mediate their investment in a public good according to the investments of others. However, most research on this topic has been conducted in artificial laboratory settings and has assumed that cooperation imposes relatively high monetary costs on players. As such, we do not yet know how humans behave when faced with non-monetary costs of cooperating in more realistic settings. Here, we present results from a real-world public good experiment where the monetary costs of cooperation were relaxed. We manipulated the cleanliness of a sink in a staff tea room (a public good) by adding or removing dirty kitchenware and then recorded the number of items subsequently added to the sink by staff members. We found that when the sink had no dirty items, people were less likely to dump their own used kitchenware and the public good was maintained. In contrast, people were more likely to dump items in the sink when it already contained unwashed kitchenware and increasing the number of dirty items in the sink led to an increase in the number of items that were subsequently dumped. This study shows that defection begets defection in real-life situations, even when cooperation is relatively cheap.