How do I did him to stop!!!! Drinking anybody cup

It don’t matter where or when if he see a cup he will drink it!! Obviously I watch him but he just will grab anybody drink yesterday at my dr I had to get weight and I turned my head for 3 secs and he drank the nurses water bottle and at my friend house she had water in a mug from painting and he drank paint water before I could get to him also he has lactose intolerance and my husband was drinking milk and left him cup on the counter cause the dishwish was full and he drink what was left and he had the worst diarrhea all day!! My mom told be to leave random cups of lemon juice around so he learns not to do that but that seems too much he has full access to water anytime he wants he has a water bottle and he gets his own water from the fridge door I sat he down many to tell him no and times outs I just at a loss