OK, a couple of points here:
1. You shouldn't use straight distilled water for fish. It contains no buffer, so will be subject to pH swings. If you want to use distilled water, you will have to add the same chemicals as if you were using RO (reverse osmosis) water.
2. Boiling water is not the same as distilling it. Distilling removes all other chemicals other than water (such as carbonates, metals, minerals).
You should get your water company's annual report to find out what is in it. If you're worried about your health, get an RO unit and use it for drinking/cooking and fish water changes (with the appropriate reconstituers).