For purifying water bleach is really a last resort. You can always boil it if you want to kill the bacterial growth wich is btw more like a diarrhea threat. I consider bleach in a preparedness point of view because it's usefull as a surface cleaner and clothing if you have been exposed to a biological terrorist attack for exemple. If you want to purify water when hiking in the mountains or there's a possibility that your airplaine crashes in the wilderness than buy Katadyn MP1 pills... Other than that, store plenty of potable water while you can. That's how I see it anyway.

Frankie