The primary element in a water molecule is hydrogen. A water molecule consists of two hydrogen atoms bonded to one oxygen atom (H2O). This simple chemical structure is vital to life on Earth. Hydrogen, being the lightest and most abundant element in the universe, contributes to the unique properties of water, including its ability to dissolve many substances, facilitating biological processes. Additionally, the hydrogen bonds between water molecules lead to its high surface tension and specific heat capacity, making water essential for ecosystems and climate regulation. Water's role as a solvent influences both environmental and physiological systems significantly.