Whatever you’re drinking, throw it away. Green tea should not taste like that, it if does, it has likely gone bad.
It’s normal for some green teas to have a vegetal flavor, in some cases even a brothy flavor, but used tank water flavor is a clear sign of a bad tea.
There is also a chance that green tea is just not suited for your pallet. It might be a good idea to try a white or yellow tea. They are made from the same plant, just processed differently.
There is a live chat on TaoTeTea.com. If you have any questions I can help you directly.