Why does water remain the same compound when it freezes or evaporates?

Water remains the same compound when it freezes or evaporates because these processes are physical changes rather than chemical reactions.1

In a chemical reaction, the constituent atoms of reactants are rearranged to create entirely new substances. Conversely, a physical change—such as the transition between solid, liquid, and gaseous states—alters only the physical properties of a substance while its chemical identity remains unchanged. Regardless of its state, water ($H_{2}O$) consistently consists of two hydrogen atoms and one oxygen atom.12

During these phase transitions, the primary change involves the breaking or forming of hydrogen bonds between water molecules, rather than the breaking of the covalent bonds within the molecules themselves. Because the internal molecular structure remains intact, water retains its chemical composition throughout these physical shifts.231