The situation that Life Hacker’s Nick Douglas presented to me was (I’m paraphrasing here slightly): hey, I’m gonna leave a glass of water out over night and I know it’s not going to be a problem after a couple of hours, but I can’t leave that water there for a few weeks can I, because it will go bad, right?

My answer (paraphrased as well) I guess it depends what you mean by bad. The water will probably taste different the longer it sits there. Yeast, mold and algae might float into it, but as far as pathogens go, my take is that it’s really low risk.

I told him that the water wasn’t the issue, it’s what gets introduced to the water like food debris or some other nutrient source. And then a pathogen. Or poop. Poop has both.

My quote was, ‘What would matter is if, like, someone had poop on their finger and stuck it in there.’

It’s not like I thought water rots, OK? I just thought that there’s enough bacteria floating around a home, or in tap water, or on your lips when you take a sip, that given a month alone in a glass, it might grow and then make you sick. But, as food safety specialist Dr. Benjamin Chapman tells me in a mildly embarrassing phone call, it won’t.

But there must be some way it could, right? Yes, Dr. Chapman says, if you didn’t wash the glass properly, and left a nutrient like juice or other sugary remnants.