In my 20s, I cohabited with a man who thought you didn’t need to wash towels because you used them when you were clean. This was someone, I should add, who graduated from both Oxford and Cambridge and now has a very high-powered job. (Not that any of that means you have an ounce of common sense, of course.) Anyway, I obviously teased him mercilessly about this. What a nitwit, I thought.

But now I have a terrible confession to make. I too am a nitwit. You see, about a year ago, I replaced my trusty clear plastic water bottle, which was super easy to clean, with one of the trendy brands made of stainless steel and silicone that everyone in my gym has. What with the gasket and the straw and the various bits you couldn’t stick in a dishwasher, it was a faff to wash. So I wasn’t very diligent about cleaning it. After all, it was just water inside, right? And water’s clean, right? I had put flavoured electrolytes in it a couple of times, but I didn’t think much about the fact that they are a tasty meal for bacteria.

Until last week, that is, when I decided to do some deep-cleaning. I stared into the abyss of my water bottle – and a terrifying amount of mould stared back at me. Mould was in the straw, in the bottle and in my insides. I am not particularly squeamish, but I squeamed. And then I started furiously Googling what sort of diseases I’d inadvertently given myself while hydrating with mould water. (The good news is that I’ll live.)

My wife, who has told me many times to wash my water bottles more often, was not particularly sympathetic when I started squealing in horror by the sink. She was even less sympathetic when I said I was going to do the world a great service and inform everyone that they should inspect the insides of their water bottles stat. Through my Googling, I had discovered that plenty other people had been shocked by how filthy water bottles can get.

“Please don’t write about this,” my wife said. “People will think you are gross and quite stupid. Seriously, this is not something you should be admitting to publicly.” She’s probably right. Still, it’s too late to spore you the details now. And while I may sound foolish, at least I’m cultured.

Arwa Mahdawi is a Guardian columnist

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