In my experience stored tap water is very safe. It gets stale and flat. I've had some strange grassy tastes show up, mostly what I assume to be algae, but the water caused no ill effects even after several years storage in less than ideal conditions. Worse case any water with an off taste can be used cooking or washing.

Given that major disease causing organisms are not in the tap water when it is stored it can, IMO, be safely assumed they won't be in water stored for long periods. There will always be some amount of bacteria and algae in the water because it is in the air but my tap water isn't nutrient-rich enough to support more than minimal growth.

That said changing out the water every year doesn't seem an unreasonable burden. And tap water, at pennies per thousand gallons, is a whole lot less expensive than commercial bottled water.