having no openings to allow water to get in

They're doing some repairs to make the roof more watertight. 他们在进行一些修理，以加强屋顶的防水性。

(of a theory, plan, or agreement) formed very carefully in every detail so that nothing is uncertain or in doubt

This book is designed to be provocative rather than a watertight piece of economic analysis. 这本书旨在引发大家辩论，而不是要对经济进行缜密的分析。

If a football team has a watertight defence, it stops an opponent from scoring a goal.

Rovers' defence will need to be watertight in their Carling Cup clash with Watford. 巡游者队在卡林杯赛上遭遇沃特福德队时防守必须滴水不漏。