Program verification is an important task since it produces reliable software. Verification of real-time control programs needs special attention since these run in the real world and it is difficult to determine their mathematical properties. Besides, validating large real-time programs manually is impossible. Owing to these reasons, mechanical program verification systems have to be used. Boyer-Moore Theorem Prover (NQTHM) which, in fact, is a generalpurpose automated theorem prover, is such a system. We corroborated the control programs of a simple real-time system, viz. a water-tank complex, using NQTHM. A useful simulator (called WATERWORKS) has been implemented for this purpose.