watertight
wa-ter-tight
adjective
Constructed so that water cannot get in or out.
"The boat's hull was completely watertight."
adjective
So well-constructed or logical that it cannot be criticised or defeated.
"The lawyer presented a watertight case."
Thesaurus
Synonyms: tight, ironclad, incontestable, bulletproof, unshakable, unassailable, incontestible