Decomposition of water is a chemical change.

The statement is true. Decomposition of water is a chemical change. On decomposition of water, we will get the chemicals such as oxygen and hydrogen.  These products can show different chemical properties than water.

$2{\text{H}}_{\text{2}}\text{O}\left(l\right)\stackrel{\text{Heat}}{\to }2{\text{H}}_{\text{2}}\left(g\right)+{\text{O}}_{\text{2}}\left(g\right)$