I make my own Colloidal Silver but I do not use tap water or even filtered water, I buy ultra-distilled water which is PH neutral and contains no floride, no heavy metals and no chlorine. The CS I make with it is 16ppm and I've never had any problems with it. I drink 30mls every day to ward off coughs, colds & flu. Ive not had any upset tummy while using it.