Tap water is monitored dozens of times daily by municipalities in every state for contaminates ranging from chemicals to microbes. In fact, the EPA’s Office of Ground Water and Drinking Water has issued extensive regulations on the production, distribution and quality of public drinking water, including regulations on source water protection, operation of drinking water systems, contaminant levels, and reporting requirements. You can find information about the quality of your tap water in the annual Consumer Confidence report that your water provider is required to distribute yearly. CRW’s can be found by clicking here . Bottled water, on the other hand is regulated as a food by the FDA and not subject to the same regulations. About 60% of bottled water never crosses state lines potentially making it exempt from FDA oversight.
Using tap water (whether straight from the tap or filtered first) is generally considered to be better for one's environmental impact than habitually drinking bottled water, because the bottling and distribution of bottled water consumes resources and produces emissions (electricity and oil to make the bottles, diesel fuel to truck the filled bottles through the supply chain, truck exhaust, powerplant emissions, bottle recycling, and so on). In comparison, the water treatment plant activities were going to happen anyway in either case, but the other costs and effects are avoided in the tap water case.