Well, mine have never drank that much! My pair usually go through 1-1 1/2 water bottles full a week... They get alot of water from veggies too.
Are you sure your water bottle isnt leaking? If they are actually drinking that much water, it could be a sign of diabetes.
This depends, how many guinea pigs, the size of the bottle, the amount of watery vegetables/fruits they eat every day, environmental temperature and moisture.. It is difficult to say what is "too much" without first knowing all these facts.
Excess water consuption, however, is indeed something to be concerned about.