It’s a simple scenario and one you’ve probably experienced several times.
You wake from a sleep and reach for your glass of water. It’s the water you poured the day before and it has been sitting in the glass for 24 hours.
But you drink it because it’s water, and water can’t go off. Can it?
It tastes different. Not as fresh. You wonder whether you’re imagining it, so you don’t drink it all. Just a couple of mouthfuls.
So what harm have you done to yourself, if any?
The good news is you’re not going to suddenly convulse or need to bolt to the toilet. But water can go stale and, if certain, albeit unlikely, circumstances exist, this ‘old’ water can be bad for you, but not life threatening.
Here’s what has happened in the 24 hours since you poured that water. The water surface has gathered dust. Water also absorbs carbon dioxide, particles of which convert into carbonic acid.
The water’s pH value changes, causing it to taste different. The word ‘flat’ is a common description.
If you sipped from the glass 24 hours earlier when you poured it, there’s a likelihood that microbes from your lips and saliva have ended up in the water, and as the water warms, these microbes multiply.
This also explains why the water may taste different and this difference can be detected as soon as 12 hours after it leaves the tap. But will it harm you?
No, 24-hour water is fine, but don’t reuse that glass without washing it.
The easiest solution is to drink water from a bottle. Sealed water won’t go stale.
If you buy bottled water – and we’re not suggesting you should, given the war on plastic – you may want to look at the expiry date. Provided the bottled water is manufactured and sealed according to health guidelines, it can last for two years or more.
Once opened and sipped, this bottle can pick up bacteria, so don’t keep drinking from it for longer than a few days, up to 12, if you refrigerate it.
But a reusable bottle, filled with tap water, and regularly washed out, is the ideal answer.
Have you noticed water left in a glass for a day or more can taste quite different? Are you careful to wash out a reuseable bottle?