Fig.: to perform humble tasks, to assist and, possibly, do the dirty work for a more powerful person. Also found in business situations, it is most often used in a political context in the sense of endorsing or promoting someone or something that in reality one does not fully support

Privately he speaks ill of his boss Mr. T. but he keeps carrying water for him hoping it would open up more interesting career opportunities

In privato critica e scredita il suo capo Mr. T., eppure continua a "portargli acqua con gli orecchi" nella speranza che gli si aprano opportunità per una carriera più interessante

The figurative use of this expression started in the late 1970s. It comes from sports, where the position of water boy - a young person charged with catering to players' comfort, including supplying them with water and the like - is the lowest rung in the team hierarchy