Hi Marita.
There is no reason why you couldn't use bottled water for your aquariums waterchanges. There's just a couple things to keep in mind:
- Find a source that will be readily available to you at all times. I mean water from the same spring, even if its bottled from the same spring under a different name. Consistency is key here.
- Once you've procurred a regular source, see if you can locate an average test result for KH and GH. I can help you in this department if you have troubles.
- Now that you have a consistent source and you know the basic chemistry of the water, you will know if you need to add any trace elements to it so that they are there for your fish.
Then again, you could always procure a good filtration unit for your wellwater and buffer it for use in the aquarium.
Either way, I will be happy to help you through the process in any way I can........
Paul