expression, ichidan verb
open up a lead; pull ahead
Idiomatic expression used in competitive contexts (sports, games, business) to describe gaining a clear advantage or lead over an opponent. Literally 'to open the water', possibly from boat racing imagery.
後半に入って、我がチームは相手に水をあけた。
In the second half, our team opened up a lead over the opponent.
新製品の売り上げで、ライバル会社に大きく水をあけた。
With sales of the new product, we pulled far ahead of our rival company.