The common name for H2O is water. Water is an essential compound for all known forms of life and is the most abundant substance on Earth's surface. It exists in three states: liquid, solid (ice), and gas (water vapor), and is vital for numerous biological and ecological processes. Water serves as a solvent, transporting nutrients and waste in living organisms, regulating temperature, and participating in chemical reactions. Its unique properties, such as a high specific heat capacity and surface tension, make it crucial for maintaining life, influencing climate, and shaping landscapes, making it indispensable for Earth’s ecosystems.