Whenever we go to the races in Joliet I travel with water tanks full only a 20 minute drive and buy water only if we run out. Headed to the race in Sparta KY about 6 hr drive no water hookup at CG bu...
So, after all this typical diatribe the answer to the OP question is,
Some folks always carry a full tank of water. Some folks never carry water or only enough for use in transit. Some folk only carry what they think they will need for the trip.