depends on the quality of water where you live i would say.i have kept well water from my cabin near the St Croix river,untreated,in a five gallon glass jug for over a year and it was good then as the day in went in..in the city,Minneapolis,i did the same thing with the same results.there are places in Minnesota,the far South West farm country,where they have a notice on the public drinking fountains and next to some creeks like the one at the Pipe Stone Quarry that the water is not fit for children,or at the quarry,dogs, to drink because of farm run off..it's so local there is no pat answer.