Mrjoeo,
I don't think that anyone really knows what causes this. You may never know.
I am using a Brita water filter. I have no idea if it does any good at all, but the water tastes really good.
After my diagnosis, I was afraid of tap water, coffee, wine and microwaves.
My doctor gave me good talking to and said that tap water was fine(as was coffee, wine and microwaves)
If the tap water wasn't fine, I guess everyone in the family would get BC...especially the people who had smoked all their lives. But, it didn't happen that way. I, who have always been so careful about everything that I touch or put in my mouth..I'm the one who got it...