Water molecules are composed of two hydrogen atoms and one oxygen atom, which are held together by covalent bonds. In a covalent bond, electrons are shared between two or more atoms, resulting in a strong attraction and a stable compound. In the case of water, the oxygen atom has a stronger attraction for electrons than the hydrogen atoms, creating a polar covalent bond. This polarity is crucial in many of water's properties, including its ability to dissolve a variety of substances and its high surface tension.