How many ounces of water is he drinking a day? It is true that it takes them longer to get water from a bottle then from a bowl. Sometimes bunnies drink excessively if they have tooth issues, or other healthy issues. So far it doesn’t sound like that, but to get idea if it is just perception of a lot, or if it really is — let us know how much he really drinks? Mark the water level with a piece of tape to help keep track.
FYI: 1/2 cup to a little over a cup of water is normal for a medium sized rabbit. It depends on their diet and eating habits. My bunny gets lots of greens (in am and pm) because she is on a pelletless diet. and so she gets much of her hydration from that. I would be surprised if she drank 1/2 cup – I barely see any change in her water level. But then on days when she eats a ton of hay (usually when I just refill her hay box), She will drink half of her water bowl.