Careful planning can increase the likelihood that a pilot study will lead to reliable conclusions and recommendations. Pilot‐plant studies are often considered appropriate or necessary for effective planning, design, and operation of water treatment facilities. By carefully planning pilot‐plant investigations before they are undertaken and by diligently conducting the study, water utility staff and engineers can maximize the return on the resources invested in pilot‐plant programs. This article contains ideas and concepts on pilot‐plant testing that have been developed through two decades of work with pilot plants.