How else would they keep you using it and buying more. Actually, what makes the water go bad, is the storage medium. In plastic bottles, the water will absorb some of the chemicals from the plastic, and taint the water. It will start to taste bad, and eventually, may become toxic enough that long term drinking, may cause cancer.
Because 'trickling' water is in motion, constantly refreshing, adding minerals, taking in ground water, rain, etc. Water in bottles is stagnate. Minerals and nutrients are nutralized by light and heat and any bacteria present will multiply in heat. Water in bottles can become stale and ick.