My guess is that your dog is drinking water as a nervous response to not being able to comprehend why the humans are moving around like that (they don't normally move like that)! Dogs with anxiety lick obsessively, tear things up, or develop other nervous 'ticks' (such as drinking water while under anxiety).
Look for other signs that your dog could be uncomfortable, and verify that this behavior is only triggered by certain circumstances (like the dancing).
If it's possible your dog is repeating this behavior more frequently (but maybe it was only first noticed during the dancing), consider a vet checkup, as it's possible there could be a more serious problem.