I take your argument and turn it on its head to argue the opposite point. Because our theoretical individual lives in the US, they have the agency to move to a place with access to drinking water.

Having access to drinking water doesn't mean it must be brought to you or even that it must be free. It just means it can't be denied, there must be a reasonable path to achieve it, I.e. access.

So when a hypothetical company called NoPont poisons an entire watershed, they're violating that right to access. When Nestlé just bottles water and sells, they're not. When Nestlé buys corrupt politicians to privatize / curtail rainwater collection so poor farmers in Bolivia have to buy water, they're very much infringing that right.