You're correct that plastic water bottles can affect water quality over time. Research, like that published in Journal of Environmental Science and Health, Part A, confirms that polyethylene terephthalate (PET) bottles may release chemicals such as antimony and phthalates when exposed to heat, UV light, or after prolonged storage. While the water itself doesn't "go bad," the bottle's material can leach these compounds, potentially impacting taste and safety under certain conditions.