While we have seen water last for many years in this type of plastic, the suggested rotation schedule is as OFTEN AS POSSIBLE. Both the FDA and Red Cross recommend that you rotate your water every 6-12 months depending on the storage condition. Water will also keep longer if you keep the tank in a cool, shaded area, like in a garage, shed, or basement. In a dryer climate, such as Utah or Nevada, fresh water may be stored for 9 to 12 months before rotating.  It's best, however, to rotate water more frequently. Depending on storage conditions and water quality, you may want to wash the tank out again every few rotations too.
There are lots of options to treat your water. The best option that we have found is the 5-year water treatment kit that we sell on our Products page called Biofilm Defender. It extends the 6–12 month recommendation to 5 years, which makes things much more convenient.
If you happen to be one of the 90% of the people who simply forget, your water will be safer for longer with a Water Supply tank because of the high-quality, non-porous plastic that our tanks are made out of. Water Supply helps make rotating water convenient by allowing you to hook a standard garden hose up to your tank. With such convenience, we suggest using your water to rinse cars, water flowers, fill buckets, and in any other situation to ensure that your water is regularly being turned.