Water is fascinating, fun, and multifaceted. Children can play with it endlessly. But play, for play's sake, is not water's only value (Crosser, 1994, Tovey, 1993). Indeed, water play is a compelling focus of study for young children (Chalufour & Worth, 2005). The concepts that young children learn from water play are essential for early childhood educators to be aware of and promote. As educational policymakers and administrators push for more well-defined assessments of learning, teachers need to be able to clearly articulate the specific concepts children learn during all types of play. This article identifies the science concepts involved in a variety of water play activities and the teacher-mediated learning "process" that can accompany and enhance this learning. (Contains 3 tables and 1 figure.)