I am sorry to hear that, that is rather catastrophic.
For your nerves and peace of mind, I did read a survey not so long ago, where Aquarians using treated tap-water were compared to people using well water, RO, natural ocean water and other sources. It did seem that people who have natural seawater had it the most easy, but tap-water users did just fine. Sometimes better that RO users.
You might want to focus on mixing up the treated tap with whatever water you already have in small doses so you can spread out the impact of the change in water quality, rather than fearing the worse and just rush into it because you are forced.
And again. I am generally sorry to hear that your place in beginning to run into real water problems, that is ofc, besides the impact on your aquaria, a very serious situation.