Water doesn’t go “bad” per se. If left in a container long enough, it goes flat (mixed in air exits) and will taste bad (compounded if stored in HDPE or other suitable plastic). The residual chlorine can evaporate from the water but I think it’s safe to assume the water won’t become infested with bugs if it was stored using reasonable precautions (i.e., don’t take a swig from the container to test quality prior to storing—backwash happens!). There may be some risk from chemicals in HDPE or other plastic containers leaching into the water during long-term storage and this can be reduced by rotation and keeping the containers out of heat/direct sun. However, I’m not convinced the benefit of rotation is worth the labor.

In essence, if water is stored for years in plastic, it may not taste very good and it may have some chemicals in it (probably less than your average pint of “fresh” strawberries), but I’m relatively certain that it will still beat the snot out of death by dehydration. If you’re worried about bugs, keep some non scented bleach on hand and dose it before drinking (but let the bleach evaporate prior to filling your cup).