a mark showing the highest level reached by a body of water.
2.
the highest point of anything; acme:
Her speech was the high-water mark of the conference.
Origin
1545-55
Examples from the web for high-water mark
Water-level data from sensors at selected locations were compared to corresponding high-water mark elevations.
Its publication was the high-water mark of the idealistic tide.
Yet this could be a high-water mark for the euro-area economy.
Yet that case was something of a high-water mark for the commission.
Legally, everything below the high-water mark is public property.
There are some who believe that the high-water mark of concern about corporate governance was last year.
Ocean cruises with moonlit decks and visits to exotic ports set a high-water mark when it comes to romance.
British Dictionary definitions for high-water mark
high-water mark
noun
1.
the level reached by sea water at high tide or by other stretches of water in flood
the mark indicating this level
2.
the highest point
Idioms and Phrases with high-water mark
high-water mark
The peak of something, especially an achievement. For example, This composition is the high-water mark of his entire output. This expression alludes to the highest mark left on shore by the tide. [ Mid-1800s ]