The inability of students to properly understand the principles underlying osmosis and tonicity leads to misconceptions that further impair their ability to apply these concepts to physiological situations. We describe a simple and inexpensive visual exercise using beads and water to mimic solutions. Using these model solutions, students will understand the concepts of tonicity and osmolarity. The hands-on exercise is supplemented with a worksheet that reinforces the concepts they learned in doing the activity. This exercise has broad application with respect to both the level of students targeted and the courses in which it can be utilized, and it is flexible enough to personalize for each situation.