as a plumbers son i can say that the purple stuff is the pvc cleaner which in necessary to help bind the pipe and i would recommend clear primer and clear glue it will have no affect on the water as that is the same situation in which you drink water in your home it will be fine. as for the hard water i live with well water and i haven't had a problem however im just now mature enough to care that my animals have exactly what they need so don't quote me but im sure hard water will be fine