Water tends to spill from a bowl and a bottle will drip. Rabbits don't tend to drink while travelling anyway.
I would recommend taking a dish or bottle with you and offering water when you arrive. If you do stop at some point, offer water then too.
You can give wet veggies to give them some moisture. Some rabbits will eat on the trip, so veggies will help with hydration. I would not give too much at once incase they don't eat it, then you don't waste to much and they don't eat veggies that have been sitting out too long.
It is good to take water from home. Enough to last at least a few days so you can transition them to the water there. Bottled water can also be good, but you might want to get the used to it before.