Water hardness in the US

I came across this map of the US showing water hardness. Since the main concern with using tap water in one’s CPAP humidification tank is around mineral buildup, I thought people might find this map interesting.

For example, I live in the northeast US, and I use tap water in my CPAP machine. I empty and rinse out the tank every day, and wash it with dish soap perhaps every few months. Upon visual inspection, I can see no evidence of mineral buildup or bacterial buildup. There is no clouding of the tank or any smell at all.

Of course, the other factor is the water treatment that your town or city does to your water. Is some places like where my father lives, I would not use tap water because they seem to use a higher amount of chlorine or something and the water really stinks.