They spread their litter and food around, spit in their water bottle, and have a very opaque, creamy urine which may contain crystals. I would not count on it, and would supply vitamin C in the form of food supplements. Adding vitamin C to the water is not as good because the vitamin C quickly degrades in water and must be replaced every 24 hours. You can also never be sure how much they are drinking. Rabbit food also contains too much vitamin D for guinea pigs and may be at toxic levels.
Guinea pigs are famous for playing with , spitting in and draining their water bottles.
Bowls, pans and crocks are not good choices for the water as they love to turn them over, chew on them and make a mess with all the water and bedding. However, whatever way the guinea pig has been raised should be continued at home. Guinea pigs can literally die of dehydration before they learn how to use a new water source. Sipper bottles with valves to prevent drainage may be helpful but spitting food into the bottle may clog it. Guinea pigs are also creatures of habit when it comes to food, and may starve to death with sudden food changes.