Water is essential for life. The brain, heart, kidneys, and lungs require continued hydration to function, and our bodies need water for digestion, nutrient absorption, blood distribution, and so much more. While water comprises around 60% of the adult body, 75% of infants' bodies are water. Children also drink more water per pound of body weight than adults, with infants consuming the most, whether through formula prepared with water or through breast milk. Because our bodies need a near-constant supply of water, the availability and quality of water are critical parts of the environment that shape child development. This is particularly true during the prenatal and early childhood periods when bodies are especially sensitive to outside influences. However, in the U.S., the systems that were once widely presumed to produce nearly universal, clean, affordable, and trustworthy water have serious gaps and challenges. Additionally, freshwater supplies are being threatened by droughts, overuse, and contamination, exacerbated by climate change. Inequities in access to clean water are the result of decisions that we have made as communities, states, and a nation. New decisions can reverse these inequities and provide all people with access to clean drinking water, with profound effects on the health and well-being of our children. This working paper from the Early Childhood Scientific Council on Equity and the Environment explores how water affects children's health, learning, and behavior, and how ensuring access to safe drinking water is necessary to support the healthy development of all children. It offers specific strategies to address disparities in access to clean water and resources to take action in your community.