@bhaaya,
Sweet, you reminded me of one of my very first experiments that I never obtained definitive data for. As a kid I was interested in survival situations and asked how long water takes to "go rotten" (because I decided the "survival kit" I was making needed some water). I was told water doesn't rot. I found this dubious and I conducted an experiment. I filled a Kraft Parmesan cheese can water and put it on a window sill.
When I checked it the water had mold floating on the surface and I was convinced I'd been lied to. Then I figured it out, the mold came from the cheese.
I learned about what makes water become nonpotable but soon lost interest and never nailed down the specifics I was looking for.
Now I finally know and another childhood curiosity is sated, thanks for asking!