If you keep using tap water it WILL DIE. STOP or kill the plant. Google Venus flytrap care.

I've started using filtered water, but will it die because I've BEEN using tap water??

Filtered water is also NOT GOOD. How is it filtered? Rain water or distilled water only.

Sorry, I meant distilled. But will it die still because I have been using the wrong water for the last three weeks?? Or do you think it'll flush out the minerals if I keep watering it with the distilled water?

Top water for a while and maybe the bad water will flush out.

Tap water is indeed very bad for the plant but no, having tap watered it in the past doesn't mean all is lost!

I bought a venus flytrap, read the instructions, said "Pft, that doesn't apply to me," watered it with tap water and slowly killed it over the course of a few months, down to the point where it had only one pathetic, dying stump of a leaf. I repotted and started caring for it properly, and it quickly started growing new healthy leaves. Your plant isn't nearly that damaged yet, so this will be an easy fix.

Here's what I did, and recommend you do:
Upend the pot and remove the plant. There's not much you can do to avoid triggering traps, so don't worry about it. Carefully brush off the rhizome and roots, cleaning off as much of the old soil as you can. Swish the roots around in a cup of (DISTILLED) water to rinse them off.
Make a new mixture of 50/50 perlite and peat moss, and absolutely nothing else. Never use any dirt or potting soil. (It's ok to reuse the pot it came in, just brush out all the old soil). Spritz/sprinkle the mixture with (DISTILLED) water while filling the pot to help get it moistened throughout. Replant your VF with the rhizomes just below the soil line and water (DISTILLED) thoroughly.

I can't stress enough that all water you use on your VF from now on must be pure distilled - not purified/spring/enriched/filtered water. (I once accidentally spilled a tiny amount of tap water into my gallon jug of distilled water, and that made my VF start dying again! It's that sensitive.)

As a final note, it sounds like you're feeding it too much, which I've read could also harm the plant, so I think you should stop for a while. Besides, you might be surprised at what it catches on its own!

Good luck!

So helpful! Thanks so much!

You're right, I think I am feeding it too much, one of the traps turned black after I fed it a big spider! I had a surplus of spiders after my husband brought up a bike that had been in a shed over the winter and there were all these spiders in it. I figured they might as well be turned into food!

Besides the one trap turning black, it's looking good. Nothing else dying. I am worried it doesn't get enough light though, despite putting it out on our balcony. I think I should resign myself to the fact that our apartment just doesn't get enough light and I can't have plants that require lots of sunlight :-(

Feeding a VFT is not necessary. Most of their energy is received by Sunlight. Bugs are like fertilizer. If the plant is outside where it belongs it'll get it's own insects easily.

If you're concerned it's not getting enough light, you could give it some artificial too. Real sunlight's always better of course, but we don't all have the perfect windows for it! I keep mine under a desk lamp with a regular CFL lightbulb (the old fashioned kind won't work) and it does okay with barely any help from the sun. :)

I think there's some tap water that might be okay. I could be wrong but apparently it does vary somewhat from city to city.

You would have to buy (around $15 online) a TDS meter to know for sure.