Is it okay if you drink ice water when you're hot?

Unless you're clinically dehydrated and/or sick to your stomach, it's just fine. Beware the Ice-cream Headache! :} If you're suffering from heat stroke, heat exhaustion, dehydration or something like that, the sudden shock of cold can make you vomit, making dehydration even worse. The trick in any case is to not drink in huge gulps, but to drink slowly until you aren't thirsty anymore.