As others have said, Princess does charge for bottled water. In fact, I think most cruise lines to. The water on board is distilled and fresh so one can just keep refilling their bottles when they want and keep them cool in their room refrigerator.
There is absolutely nothing wrong with the ship's water. I find it tastes much better than what comes out of the faucet at home. We usually carry a couple bottles of water on board, and re-fill them as needed for shore excursions.