It's the dose that makes the poison. The level of it in tap water is proven safe. If you were to consume a bucket of it, perhaps not so safe
The brilliant thing with science is it changes as we learn more. With vaccines- we already have a large body of information based on many years of research and study. And there is one thing that we DO know about them- they are safer than the diseases they protect against. Without them, you are far more likely to contract one of those diseases. With more and more people NOT vaccinating, these diseases are experiencing a resurgence. It is getting more and more dangerous to NOT vaccinate. There is SO much evidence for this.