A good source of spring water. You may even be able to bottle your own for free, but (as per your question), if we assume you can't, you may still be able to find a distributor (a company that delivers water to homes and businesses) of good spring water close by. To me this makes a lot more sense- just bottle good water at its source instead of worrying about filtering it.
Consider the normal alternative- take (polluted ?) water, filter it some, add a bunch of toxic chemicals to kill pathogens, and send it to your home. At that point you have to filter at the toxic chemicals they added in addition to what might be existing. And filtering out fluoride is a pain. By the time you are done filtering (this is very true in the case of reverse osmosis) you have a mineral-depleted water that needs to be re-mineralized to avoid losing minerals every time you drink water. Spring waters generally has very high amounts of minerals so you can actually gain them as you drink water.
I am lucky to live somewhat close to what some consider one of the best spring water sources in the world, so I get a lot of good minerals without having that bad of an environmental impact. Of course I am using the re-usable large water jugs, so no plastic being thrown away. And I am within walking distance of a distributor, so I get a big discount for picking up the water myself.