I think because rabbits in the wild are dawn/dusk animals, they're just not built for this heat. they'd be under in the ground where its cooler, snoozing the day away. I'm not sure if its a cause for concern since mine don't tend to eat much when its hot, but then perk up when its cooler in the evening.
plus the sudden change is hard for them to adapt too as well.
that being said tho, I'd remove the icecubes from the water and leave them with cool/room temp water. I honestly can't find anything on it now (sods law) but its not recommended to give bunnies ice cold water or ice cubes, as the temp different between them and the water (or ice) has been known to cause stasis. I'm sure there was something possibly from the RWAF but I can't find it anymore.
theres been some research to suggest in humans that drinking cold drinks won't actually help cool you down, a lot of the time it can do the opposite and warm you up. its due to the cold having a cooling affect in your body, so your body rushes to warm you up further. drinking hot drinks can actually help cool you down, as you then sweat it out basically. of course I'm not suggesting to give a rabbit a cup of tea :lol: but giving them ice or cold water will probably make them hotter. in humans the affect is somewhat minuscule (depending on how much you drink, because we're larger than rabbits), but the affect on rabbits could be bigger. just something to thing about!
its far better to wet them down than it is to give them ice cold water imho. so I'd suggest damping you hands and getting their ears wet. their ears are thin and have the blood vessels closest to the skin, so it will help cool them down far more than ice water would. you could also dampen your hands and run it over their body. they don't like it, but its a good method of helping keeping them cool