My tap water alters through the year, and depending on what the water company is doing. I have tested GH and KH at varying levels from 3 degrees to 5 degrees. Most of the time it is 4 to 5 degrees. The one time it tested at 3 degrees was a bit of a surprise.
The water company alters the pH with sodium hydroxide, and it usually tests in the upper 7s. A friend on a related water supply tested the pH at 9.0 one time. I have seen mine in the upper 8s, but not often. The pH in my tanks will drop when I use a high CEC substrate. I wonder if the substrate is removing the sodium hydroxide? I KNOW it is removing the carbonates.