I took Elijah to a paediatric gastroenterologist about his reflux when he was four months old and he said that at four months of age, it's okay to start introducing them to tap water. They have to start building their immunity and resistance to things - apparently in poorer countries, their bodies handle illness much better as they have better resistance from the exposure they already have... whereas in more sterile environments, if you keep people / babies in sterile environments, it makes it worse when they do get sick, as their digestive system tends to cop it worse, with intestinal infections etc. So I stopped sterilising from then, everything goes in the dishwasher which is very hot anyway. It's another reason I hate antibiotics, and only go for it if myself / kids are really not coping with pain relief.