If you are concerned about the shelf-life of water in 5-gallon jug, technically speaking, water doesn't have an expiry date. However, unless you are storing the water jug in a climate-controlled environment, it is not advised to leave water that has been exposed to air indefinitely or for a longer period. Water can stay good in a 5 gallon jug for at least six months before you replace the water jug. Generally, the sooner you use the water and replace them, the healthier and better it is.