Past decade all i drink is purified water, no tap/no spring. i heard that p water can kill brain tissue/cells and is bad for you.is p water safe?

Pure water is fine: A normal person drinking normal amounts of purified water, good quality tap water, good quality spring water, or good quality bottled water... should notice no ill effects from drinking that water. The water is fine. Without water like that, our species would quickly go extinct. Normal amounts of water, drunk by a normal person, does not kill any cells or tissues.