Nobody is ever likely to accuse Bear Grylls of being a wimp. When it comes to grit, courage and good old derring-do, the veteran adventurer’s credentials are close to impeccable.

Let’s have a quick look at his CV. Climbed all the way to the summit of Everest just 18 months after breaking three vertebrae in a horrific parachuting accident? Check. Braved force 8 gales and dodged icebergs while crossing the North Atlantic in an inflatable boat? Check.

Rolled up his sleeves and stood shoulder-to-shoulder with the big boys of the SAS? He’s got the T-shirt for that as well.

All things considered, it is probably fair to assume that Edward Michael Grylls isn’t the sort of chap who has ever felt the need to sleep with the lights on.

Yet, if his recent comments are to be taken at face value, one of the few things that actually rattles him is the prospect of drinking a glass of British tap water.

Grylls certainly didn’t mince his words when he addressed the issue this week. ‘The long-term health effect of poor quality tap water is horrendous,’ he remarked.

While he conceded that UK tap water is relatively good compared to what is on offer elsewhere, he also insisted that it is ‘still terrible’.

The long-term health effect of poor quality tap water is horrendous, says Bear Grylls

Speaking about the chemicals used in the water treatment process, Grylls added: ‘It’s universally acknowledged chlorine is going to kill bacteria and parasites, but it’s not going to be good for your health.’

It could be argued that Grylls’ words carry even greater weight given his previous form for slaking his thirst by drinking – among other delights – his own urine and the juice squeezed out of elephant dung.

Either way, it is hardly the sort of ringing endorsement that Britain’s beleaguered water industry could do with right now.

Observers will rightly point out that the 50-year-old has skin in the game on this occasion, though. His comments were made in the context of his work with a British company that sells £129 water filters. Against that backdrop, a cynic might be forgiven for thinking that Grylls’ concerns are not entirely unrelated to the fat fee he can no doubt expect for lending his name to the enterprise.

However, none of that takes away from the fact that very real fears exist about the nation’s water supply. There have been repeated ripples of outrage about rising domestic bills, uneven service and the vast sums pocketed by the executives running even the most inefficient water companies.

But the anger would undoubtedly be rather more muted if it wasn’t for the growing anxiety about what exactly is coming out of our taps.

Earlier this year, analysis revealed that raw drinking sources across England are polluted with so-called ‘forever chemicals’. Numbering around 10,000 in total, these perfluoroalkyl and polyfluoroakyl substances (PFAs) are used in the manufacture of everyday products such as frying pans, carpets, cosmetics and food packaging.

They have been linked to a range of conditions including several types of cancer, reduced fertility and Parkinson’s disease. Perhaps even more worryingly, their nickname comes from the fact that there is very little evidence to show that they biodegrade over time.

Analysis this year has revealed that raw drinking sources across England are polluted with so-called ‘forever chemicals’

Tests carried out by a team of experts from the University of Birmingham found ten target PFAs present in 99 per cent of water samples – both tap and bottled – taken from cities across the UK and 14 other countries. Describing them as ‘silent killers’, Professor Luisa Orsini, from Birmingham’s School of Biosciences, remarked: ‘They have very strong adverse effects over time even at very low doses – and that’s the message we want to share from our research.’

According to experts, PFAs pose a double threat to the public because our water treatment systems aren’t advanced enough to eliminate them and there is insufficient regulation.

While moves are underway to bring in legislation to safeguard against the worst effects, it may already be too late for many. Professor Ian Cousins, an environmental scientist at Stockholm University, and one of 50 experts to write to the Government urging stricter rules on the chemicals, has said: ‘Because the UK has been slow in acting on PFAs pollution, many British people have been unnecessarily and unknowingly exposed to a whole cocktail of PFAs.’

But if PFAs are a more recent threat, they join a long list of other concerns.

It is less than a year since a damaged air valve in the South West Water network resulted in cryptosporidium – a parasite that causes diarrhoea as well as stomach cramps and vomiting –getting into a reservoir near Brixham in Devon. The result was more than 50 people falling ill and 17,000 homes left without water for eight weeks.

Shortly after that, the perpetually-embattled Thames Water – Britain’s biggest water firm – gave a ‘precautionary’ warning to more than 600 households in Surrey against using their domestic water supply for drinking, cooking or brushing their teeth. It came after more than 2,000 litres of petrol leaked into a stream from an Asda Express filling station.

Meanwhile, authorities issued a ‘boil water’ notice to customers in ten areas of South Wales last November following a contamination scare at a treatment plant amid flooding caused by Storm Bert.

None of which inspires confidence – especially against the backdrop of Environment Agency figures that show storm overflows spilling sewage into our rivers, lakes and seas for more than 3.6 million hours last year.

And if all that wasn’t enough to be worrying about, concerns are also growing about the presence of microplastics in tap water.

Equally, though, there is a school of thought that reckons critics of our tap water are – for want of a better expression – taking a glass-half-empty view of things. According to Water UK, the trade association for the industry, almost 16billion litres of water is treated every day before being supplied ‘directly to almost every household across the country’.

It adds: ‘This water is treated to some of the strictest levels in the world and passes over 99.95 per cent of tests.’

Our tap water is routinely ranked highly for quality in international assessments carried out under the auspices of America’s prestigious Yale and Columbia universities. In its latest annual report, the Drinking Water Inspectorate (DWI) – an independent regulator that is part of the Department for Environment, Food and Rural Affairs (Defra) – also gave its stamp of approval. The quality of water in England is ‘excellent’, it found, with ‘public supplies consistently meeting the stringent regulatory standards’.

Academic Peter Jarvis, professor of water science and technology at Cranfield University, put it in more forceful terms this week. ‘We do not want people to think that tap water is unsafe to drink... the UK consistently is in the top five in the world,’ he said.

‘Where chemicals are added to tap water, this is always done to ensure the safety of the water, and using levels that are safe to drink, with significant margins of error factored in, so there is no real need to filter these out.

‘The benefits of adding chlorine to tap water significantly outweigh any of the often unproven negatives.’

So, some words of reassurance for anyone who fancies filling a glass from their kitchen tap.

But perhaps not a sentiment that Bear Grylls is likely to drink to any time soon.