If chloramine in tap water kills naegleria fowleri why is it advised not to get water in your nose when showering?

Balance: Water by itself is not a balanced solution that would not irritate the inside of the nose. Nasal wash/netty pot solutions have minerals added to balance them so they do not irritate. Solutions that have too many or too few minerals upset the balance of this fragile tissue. The same would go to avoiding chlorinated pool water while swimming.