How long can you keep water in a sealed bottle? RV tanks are not sealed though, but water is water. Water doesn't go bad. What does go bad is how quick bacteria grow in the tank, (or that sealed bottle of water). And that duration depends upon how pure the water is to start with, what kind of bacteria is already growing in the tank, and outside temperature. Warmer temperatures will cause bacteria growth quicker than cold temperatures.
So, really, its a question that only you can answer, based on your own tank, temperature, existing bacteria in your tank, and the purity of the water you put in to start with.
