As far as I understand, if one takes an empty clean container and fills it up with tap water, the shelf-life is somewhere in the vicinity of 6 month.
This will most likely vary depending on storing conditions/environment. I.e., if its hot - water will go bad faster, if cold - slower.
One way to remedy this situation is to use Water Preserver . It can keep water bacteriologically safe for a very long time without the need for change. Actually only rated for 5 years, but it was tested for as long as 8 years or longer.