When it comes to describing something as "most water-resistant," there are a few other synonyms that can be used to convey a similar message. For instance, the phrase "highly impermeable" or "extremely waterproof" can both indicate that the item is resistant to water to a great degree. Similarly, "superbly watertight" and "exceptionally hydrophobic" can both suggest that the object is able to repel water with ease. Other possible synonyms include "outstandingly rainproof," "superiorly sealed," and "eminently moisture-resistant." Ultimately, the key is to choose a synonym that conveys the desired level of water resistance in a clear and concise manner.