I went to Costco and can't understand why everyone was buying the same thing

Almost every trolley we walked past had the same thing inside - some of them piled high with multipacks

I know, I know - I said I wasn't going to go shopping at Costco on a weekend again after my last experience... but Saturday was the only day we had time last week. And to my surprise, the queues weren't so bad.

We filled up on fuel on the way in, saving 9p per litre compared to our local petrol station in Birmingham, and nabbed a car park space on the first row we drove down. After scanning my husband's card at the door, we zipped through the electronics section, past huge flat screen TVs and shiny iPhones.

We skirted the aisles filled with sports equipment, suitcases, stationery and kitchen supplies, only slowing down to browse when we reached the grocery department so we couldn't be tempted into any extravagant purchases. As we squeezed our way through the maze of industrial-sized shopping trolleys to reach the bakery section, I noticed something.

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Almost every trolley we walked past had the same thing inside - some of them piled high with multipacks, the customers pushing them clearly struggling under the weight of packs upon packs of bottled water.

As a tap water drinker, and one that mentions how superior Birmingham's is whenever the topic comes up in conversation (and sometimes even when it doesn't), I was baffled why the bottled version was proving so popular. Yet every aisle we turned down seemed to be crowded with shoppers stocking up on plastic-wrapped slabs of the stuff.

Costco was clearly supplying to demand. Around the corner, we stumbled across a whole bottled water section, with hundreds of packs of Highland Spring, San Pellegrino and Costco's own Kirkland brand stacked as tall as me.

I had to admit, the prices were very reasonable - £5.62 for 12 x 1.5 litre bottles of Highland Spring, when six cost £4.10 at Tesco. The own-brand versions were even cheaper at £4.18 for 40 x 500ml bottles.

It wasn't enough to convince me to load up our trolley, not when the free stuff at home is so tasty, but if you do prefer bottled, I can see why you'd head to Costco to stock up. Personally, I was more impressed by the 600g tubs of Marmite, the painter's buckets of Hellmann's mayonnaise and the ginormous pizzas I'd probably have to fold in half to fit in my oven.