Teachers can use inquiry to make sure that student learning is hands-on and minds-on. There are many levels of inquiry and teachers can even include some of their favorite cookbook labs after modifying them. Inquiry does not always mean lots of time, money, materials, and mess. One of the most important things that inquiry does require of teachers is thinking about how you will question students. Questions need to be designed to do one or more of the following: engage the learner, explore misconceptions, assess current understanding, encourage application of the material to a new situation, and collect feedback. Transforming instruction to inquiry is a gradual process that takes reflection and planning. This article describes a favorite tried and true classroom activity that asks students to purify a sample of water. After a short narrative describing a fish's journey downstream past various sources of pollution, students are presented with a focus question, "Which is the best method to clean pollutants from a sample of water?" that will require them to apply what they have learned about filtering and distillation to a new situation.