Agreed. Tap water can contain a good deal of CO2. The same for well water. I've got well water going through an RO system, and even after the RO the water still contains CO2.Indeed it does and that's a fact. Tap water can contains a good amount of CO2 due to how the water is processed in water plants before it is sent back into the pipes. This is not intentional but a consequence of the water treatment processes.
Many people make the mistake of testing pH right out the tap. It's always best to fully degas and age it for a few days. And it can cut both ways.
Sometimes there is CO2 added which lowers pH, and there can also be other things (like sodium hydroxide) added that raise pH. Either way best to let a sample to come to equilibrium with atmosphere before testing.