Baby won’t drink water

My son will be 6 months next week, his doctor recommended an ounce or 2 of water for constipation and he absolutely hates water and won’t drink it. I even tried putting it in a sippy cup that he likes to hold and chew on and he just looks disgusted and spits it out. He’s on day 2 of not pooping (he’s formula fed) and I can definitely tell his stomach is starting to bother him, I’ve tried belly massages and bicycle kicks for the last 2 days and nothings working. Any advice? Either on how to help him poop or how to get him to drink some water? I’m not really sure what to do at this point.