Someone Argues That He or She Doesn't Drink Tap Water

Someone argues that he or she doesn't drink tap water because it contains thousands of molecules of some impurity in each glass.How would you respond in defense of the water's purity,if it indeed does contain thousands of molecules of some impurity per glass?

A) Impurities aren't necessarily bad,in fact,they may be good for you.
B) The water contains water molecules and each water molecule is pure.
C) There's no defense.If the water contains impurities it should not be drunk.
D) Compared to the billions and billions of water molecules,a thousand molecules of something else is practically nothing.