Storage of Fresh Water - How Long

I live in Florida and do not have to worry about my tanks freezing. For this reason I never empty my fresh water tank or water heater. I have treated municipal water and I top the tanks off with as much water as they will hold to minimize oxygen in the tanks that could promote the growth of bacteria. This also gives me a reference to check to see if there are any leaks in the system. I do have an under counter water filter and I have never noticed any difference in the taste of the water from it sitting. Since we occasionally have hurricanes in Florida our RV is our lifeline if a storm hits