This experiment can lead nicely into a social studies unit about the importance of water to human communities. It could also be used as a starting point for a discussion of how scarcity affects price.
I like this activity because it works well for a wide variety of students. For students who are easily overwhelmed reduce the number of scents to match. High level students could be asked to come up with an idea for another experiment like this one but for a different sense. Consider allergies when you plan this activity!