Is water a lubricant?: Inquiring about a dilemmatic statement in physics education

We designed an inquiry activity to investigate the question, 'Is water a lubricant?' Placing the same object on surfaces of three different materials, we observed the effect of adding a small amount of water on the coefficient of static friction, μ_s. Up to 1 ml of water was added. The results of each surface were graphed and compared with one another. In general, our findings show that the addition of water serves to increase μ_s up to a certain point, before decreasing it. The experiment can be easily replicated in a secondary school science lab. It presents two seemingly opposing phenomena, but they both hold because they occur within their respective boundary conditions.