Listener Isla, 11, wants to know if bottled water from the UK's biggest selling brands such as Evian and Buxton is cleaner, healthier, cheaper and greener than the stuff that comes from the tap.

Greg Foot drills down into the subject, investigating the claims made by manufacturers of bottled water. Does it make any difference if water has spent years underground being "filtered by rocks" before being bottled? Are there more minerals in bottled water than in tap? And even though companies are making more of their bottles from recycled plastic, what’s the environmental impact?

Greg speaks to experts including a lecturer in water chemistry, an environmental NGO and a water sommelier (yes, they’re a thing!) who explains why some bottled water can cost more than a hundred pounds.

This series, we’re testing and investigating your suggested wonder-products. If you’ve seen an ad, trend or fad and wonder if there’s any evidence to back up a claim, drop us an email to sliced.bread@bbc.co.uk or you can send us a voice note to our WhatsApp number: 07543 306807.

PRESENTER: Greg Foot PRODUCER: Simon Hoban