Yep -- try straws (get colorful, fun ones or even squiggly straws-as long as they aren't hard for him to sip through); keep offering; keep feeding healthy foods that are watery. Please stick to your guns about not offering him chocolate milk and lots of straight juice! That develops a kid's "sweet tooth" and you are right that once you start that, it sets a precedent and they don't want to go back. I think the toddler stage of "I hate drinking" is one reason our niece, now 11, will drink only chocolate milk, hot chocolate and sodas -- she despised water and plain milk as a todder and frankly, her parents indulged her with whatever she would drink as long as it was liquid -- and now she guzzles only sweet stuff. She finally started drinking water more as she got older but she definitely was indulged into a wicked sweet tooth and still is allowed to drink a lot of junk.
Popsicles are great but please don't get store-bought ones; they are pure sugar and artificial colors. Make your own with well-watered juices or even with plain water -- some kids love the idea of ice more than the idea of water. Be sure he can't bite off chunks, though, because that could be a choking hazard. You can get popsicle "molds" online and even at many grocery stores.
Meanwhile, ask your pediatrician for ideas if you are concerned about dehydration. I guarantee, the doctor has seen this many times before and will have suggestions for foods and other strategies. It's not at all unusual for a kid this age to dislike fluids. I think they often dislike the "texture" of fluids and feel like "I'm going to gag because it's too thin" though they don't say it that articulately!