Contrary to popular belief, boiling water doesn't remove chemicals/minerals. It just kills off biological impurities like microscopic single celled organisms, bacteria, and viruses. Hence why its said to boil any water you gather from streams, rivers, lakes, etc before drinking it.
Also, as Adelae says, it also boils off some of the pure water, but not the impurities, leaving the remaining water to become more concentrated with said impurities and raise the ppm.
This is actually part of the distillation process in action. The water, that is to say the hydrogen and oxygen molecules that it's comprised of, will turn into water vapor, leaving behind the impurities. If cooled down enough the water vapor will then condense as pure H20. This condensation is collected in a separate container and becomes known as Distilled or pure water. The impurities are left to boil down in the first container until no hydrogen and oxygen molecules are left and only the impurities remain.
"FEED ME!" - Audrey II, from Little Shop of Horrors