It’s not the water I’m worried about

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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. 

But even if you’ve drunk out of the glass, getting your mouth on it, leaving a lip print, and then leaving out the glass — even then, he says, you’re not going to poison yourself with your own mouth bacteria.

Obviously, if the water supply is contaminated, all bets are off. If it was toxic when it left the tap, it’s still toxic after sitting out. But apparently, as long as it started out fine, even super-gross-tasting old water is healthy to drink, and I’m an ignorant hydrophobe. Fine. But I’m not alone. I only got curious because cooking blog The Kitchn asked the same question — or maybe they were stating the obvious for rubes like me.
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About Ben Chapman

Dr. Ben Chapman is a professor and food safety extension specialist at North Carolina State University. As a teenager, a Saturday afternoon viewing of the classic cable movie, Outbreak, sparked his interest in pathogens and public health. With the goal of less foodborne illness, his group designs, implements, and evaluates food safety strategies, messages, and media from farm-to-fork. Through reality-based research, Chapman investigates behaviors and creates interventions aimed at amateur and professional food handlers, managers, and organizational decision-makers; the gate keepers of safe food. Ben co-hosts a biweekly podcast called Food Safety Talk and tries to further engage folks online through Instagram, Twitter, Facebook, YouTube and, maybe not surprisingly, Pinterest. Follow on Twitter @benjaminchapman.