Is ATP hydrolysis reversible?

Yes, ATP hydrolysis is reversible.

ATP (adenosine triphosphate) is composed of a ribose sugar, a nitrogenous base (adenine), and three phosphate groups linked together by high-energy phosphoanhydride bonds. 

During ATP hydrolysis, water breaks down one of the three phosphoanhydride bonds, releasing one phosphate group as well as the energy stored within the bond. The AMP (adenosine diphosphate) molecule left behind contains only two phosphate groups. 

In the reverse reaction, energy is used to add a phosphate group to AMP and convert it back to ATP.