Why is it possible to get nargleroa fowleri from city tap water? doesn't chlorine kill it?

Not from tap water: Many things are possible in life. The chances of catching brain-eating amoeba from tap water in the U.S. is so unlikely that the answer is "no". If the water's chlorination or disinfection became inadequate, it's possible that Naegleria could survive in that water. The level of chlorination should remain high enough all the way to one's tap, as Naegleria cysts are somewhat resistant to chlorine.