Source : WordNet®

watertight
     adj 1: having no leaks [syn: {leakproof}]
     2: not allowing water to pass in or out
     3: without flaws or loopholes; "an ironclad contract"; "a
        watertight alibi"; "a bulletproof argument" [syn: {ironclad},
         {unassailable}, {unshakable}, {bulletproof}]