plowing water

plow water

To pursue or continue with some futile task or activity, wasting one's time as a result. Usually used in the continuous tense. I've spent my life campaigning for environmental protection, but with the way the world's governments continue to favor corporations over everything else, I feel as though I've been plowing water this whole time. You're plowing water if you think you're going to change Henry's mind.
See also: plow, water
Farlex Dictionary of Idioms.

plowing water

n. wasting time doing something futile. You’re wasting your time. You’re plowing water.
See also: plow, water
McGraw-Hill's Dictionary of American Slang and Colloquial Expressions
See also:
  • plow water
  • run in circles
  • be running around in circles
  • be spitting in the wind
  • be spitting in(to) the wind
  • spitting in the wind
  • be pissing in(to) the wind
  • go (a)round in circles
  • go around in circles
  • go round in circles
References in periodicals archive
* plowing water: To do something that has no lasting effect; such as working on a project that makes no meaningful contribution.