howlong can rain water sit before use?

hey does anyone know howlong rain water can sit in a barrel/tank? cuz in the beginning of the season i won't be using as much water so some might sit but so some might sit up to 4or 5 days what do guys think i should prob use a air stone right but its in the woods so no power for air stone anyone got any ideas for someone trying to get by on mostly rain water where i am it would be tough and almost impossible to carry/drive water to where i am i thought about running a hose but to risky

4 or 5 days hmmmmm. if the temps are in the 80f then I would pass any longer then 4 days . 3 to 4 days tops 80f unless you can put your hand in it and smell it if it smells clean and clear it will be ok . if it stinks like sulfer or funky you have to pass. it may be fine. if its covered it should be ok as well. I drank a old water I opened it 2 weeks ago and recapped it up and it sat for weeks and it was in the 90f I drank it ! and said shittttttttttt . I never got sick . so I think if it don't smell like but funk use it

You could use H2O2 and keep it longer...the oxygen will kill off the buggers....