Can the learner perform the behavior with another person? A different place?  A different time? Does the person perform the behavior if you change the instruction a little?   Can he now ask for water in more than just one way? These questions tap into the generalizability of a learned behavior.  In an ABA-based intervention, being able to generalize learned skills by being able to perform the behavior in slightly different conditions OR the learned behavior having slight differences without teaching is crucial.