Yet more water weirdness

I recently posted about an apparent crash of my bio filtration
in two tanks. Today, I tested a 20G tank 24hrs after a 80% PWC,
and was fairly surprised to see an ammonia reading of 1.0 (using
AP 2-reagent test, whatever that's called).
On a lark, I ran the test on some water fresh from the tap, no
treatment of any kind. The reading was 1.0!
Wow, could that test kit be bad? So I ran a test on some
bottled spring water, and got a more sensible reading of 0.0.

What does all this mean? Could there be that much ammonia
in tap water?!?

Gunther, who now thinks maybe stamp collecting would be
a less stressful hobby.