Whisk together the water and flour in a small bowl or glass measuring cup, making sure there are no lumps and no flour sticking to the bottom. Set this thickening slurry aside until needed.
Pour chicken broth into a medium sauce pan, and bring to a boil over medium heat.
Add the onion powder, whisking ’til dissolved, and cook another 1 to 2 minutes.
Whisk your slurry mixture into the boiling broth, stirring constantly ’til the gravy thickens. It should start to thicken right away, but if for some reason your gravy is too thin, you can whisk another tablespoon of flour into a tablespoon water (making another slurry), and add that to your gravy to help it thicken up more.
Add your salt and pepper, to taste.
Serve the warm chicken gravy with your dinner.