I moved to a new city recently, and where I lived before I never had any issues with ammonia in my tap water. However, where I live now does have about 0.5 - 1 ppm ammonia in the tap water. Ammonia is very toxic to fish, and even more toxic at a higher pH. My pH is rather high at 8.0, so I have a bit of a problem on my hands!
Thankfully, it's not the end of the world because there is a fairly simple solution. I have always used Seachem Prime as my tap water dechlorinator, but in addition to removing chlorine and chloramines, Prime also has some other beneficial qualities. It is capable of detoxifying ammonia, nitrite, and nitrate for up to 24 hours. At the regular dosage, Prime efficiently detoxifies 1 ppm of ammonia, and in an emergency, it can be safely used up to 5 times its normal dose. When the ammonia is detoxified, it remains in the aquarium in a
non-toxic form, so the biological filter can still convert the ammonia
to nitrites and then nitrates.
So there's my solution! I already used Prime anyway to remove the chlorine from my tap water, and now I can keep using the dosage I've always used to additionally detoxify the 0.5 - 1 ppm of ammonia in my tap water. Of course, Prime's detoxifying properties will wear off after 24 hours, but within that 24 hours, the biological filter will have converted it to nitrites and then nitrates anyway. I have tested the tank water for ammonia the day after doing a large (90%) water change, and sure enough, the ammonia is down to zero.
Cheers to simple solutions! :)