The phrase "as watertight" is correct and usable in written English.
It is typically used to describe an argument, plan, or explanation that is very strong and unlikely to fail or be challenged.
Example: "The lawyer presented a case that was as watertight as possible, leaving no room for doubt in the jury's mind."
Alternatives: "foolproof" or "ironclad".
Their logic is about as watertight as that of the Canadian policeman.
As the committee's chairman, I am concerned with ensuring that government legislation is of high quality and is as watertight as possible.
The remain camp's strategy could yet pay off, but its case is not nearly as watertight as Cameron and co think.
Their defence is as watertight as a colander and the two strikers they started here boasted just two goals between them.
Verdict: David Cameron has broadly got what he promised, but has to phase some benefits back in and the deal isn't as watertight as he wanted.
It is very difficult to build and maintain a system which protects us effectively against every possible likelihood of attack, but we will not rest until we have controls that are as watertight as possible.
In addition, the ship was equipped with notable safety features, such as 11 watertight compartments as well as radar, which was then a relatively new technology.
The more reasonable divide over the treaty was whether America should act like a sovereign state, rejecting an agreement that was not watertight as far as its own security was concerned, or whether it should, despite that, satisfy its allies by ratifying it.Those senators who voted against have been condemned, not least by President Clinton, as isolationists.
The technique requires extensive surgical exposure in order for the sutures to be watertight as well as an additional incision for harvesting the periosteum.
On some occasions it is prudent to withhold judgment until the case is as close to watertight as possible; on others a precautionary principle means we should act even when firm proof is lacking.
A segmented tunnel is generally constructed as a watertight tunnel with a certain amount of allowable leakage.
