Facts & Figures

The fact & fiction surrounding Bath’s most famous asset!
The fact & fiction surrounding Bath’s most famous asset! 1024 1024 mike@savouringbath.com
Is it heated by volcanic activity?  Does it heal wounds and illness?  Are they the only hot springs in the UK?
Bath’s thermal water springs have been a source of myth and legend for over 2000 years but let’s bust some of the popular myths surrounding them!
The Cross Bath

The Cross Bath

Firstly, the definition of a ‘natural, thermal spring‘ seems to be a matter of debate as there is no universally accepted definition.  There also seem to debates about the differences between, ‘hot‘ springs, ‘warm‘ springs, ‘thermal‘ springs amongst other terms.  Nonetheless, reading what a large range of geologists have to say about it, the most accepted definition of a ‘natural, thermal spring‘ can roughly be summed up as:

“water reaching ground level, at a temperature above human body heat (37.5C) and where the temperature and course have not been influenced by human intervention but by nature (i.e. geothermal)”

Now don’t quote me on that because it’s my own (convoluted!) definition, and as someone who is in no way a geology expert, I’m really not the right person to open a debate about it!  But it’s the definition I tend to use to describe Bath’s springs, and it’s based on a widely disputed series of definitions you’ll easily find all over the internet and in literature on geology.  But if we take this as a generally accepted definition, then we can safely say that Bath’s springs are the only example of their kind in the UK & Ireland.

Nonetheless, there ARE other warm water sources in the UK!  For example, the nearest to Bath is at Hotwells in Bristol (~12 miles to the west of Bath) which, like Bath, was popular with visitors during the 18th century.  There is still a spring at Hotwells today but the temperature is ~25C and nowadays it trickles out onto the mudflats of the River Avon.  This is sadly pitiful compared to the constant flow we get in Bath, of over 1 million litres per day.  So I’m afraid Hotwells and many others wouldn’t qualify by some definitions of a thermal spring.

The King's Bath

The King’s Bath

This depends how you look at it!…

Firstly, it’s important to point out that there are 3 natural thermal springs in Bath: The Cross Bath, The Hetling Spring, and the King’s Bath.  There are also many, man-made boreholes which have been cut into the earth around the city centre over the years, to tap into the hot water… but lets not confuse things by talking about those!

  • The King’s Bath is the largest spring and can be seen during a visit to the Roman Baths Museum, but it is neither accessible, nor suitable for bathing;
  • The Cross Bath is a private bathing facility operated as part of the Thermae Spa;
  • The Hetling Spring is not visible to the public as it is in a vault beneath a city centre street.  A borehole cut to the Hetling Spring a few years ago, now provides water to the private bathing facility in the Gainsborough Hotel.

The temperature of each of these 3 springs is actually slightly different by a matter of a few degrees celsius.  Records over the years show little variation so it’s not untrue to say that the temperature of the thermal water is reasonably consistent.  But the temperature of each spring is different so saying that the springs are all the same temperature as one another, is not true.

According to a document published by Baths Environmental Services team, the hottest of the 3 spring is the Hetling Spring at 46-47C.  The smallest spring is the Cross Bath at 44-45C, and the largest is the King’s Spring which is a temperature somewhere in between the other two – these temperatures are based on records over the last ~100 years.  So in fairness, saying that the water is 46.5C is not inaccurate, but it is just a rough average between each of the 3 springs true temperatures over time.

I live in Bath… and I’m very happy to go to sleep at night on the general understanding that we don’t currently have any volcanoes here!  However, while ‘volcanic activity’ may not be an accurate term, when we’re talking about heat coming from the ground beneath our feet, it’s not too far off.  But if we just say that the water is heated by volcanic activity, that would be misleading.

Surrounded by hills: Bath sits in the bowl of the Avon valley.

The City of Bath is at the bottom of what I like to describe as a huge natural amphitheatre, and that’s easy to appreciate if you stand in certain parts of the city centre and look between the buildings at the hills which mostly surround the city.  This may well be the remains of a crater (caldera) of a long extinct volcano but we’d be talking so far back in time that it becomes pretty irrelevant to use that as a point of reference when describing the nature of our hot water.  It’s actually widely accepted that Bath’s thermal water once fell as rain (‘meteorological water’) much more recently.  This rain water fell on the Mendip Hills south of Bristol, in north west Somerset around 8,000-10,000 years ago.  The Mendips are mostly formed of carboniferous limestone.  Over time, limestone reacts with water by dissolving, leaving behind spaces in the rock, and increasing the mineral content within the water.  As a result of this, the Mendips are now highly populated by underground cave systems and rivers which have become famous, such as Gough’s Cave and Cox’s Cave at Cheddar Gorge, Wookey Hole, and various others only accessible by experienced speleologists.

Geologists predict that the rainwater in our case, reaches a depth of somewhere around 2.5km below the earth’s surface, and the deeper you get, the warmer it gets.  Subsequently the water is heated to temperatures which almost make the water boil.  This creates pressure, pushing the water back up a geological fault in the rocks below Somerset, called the Pennyquick Fault.  The water travels along this fault and emerges in the city of Bath where we have our springs!

The heat which causes the temperature of the water to be high, is a result of what’s known as the geothermal gradient.  This describes the rate at which the temperature increases based on depth below the earth’s surface.  Geologists have made predictions based on the temperature of the water at the surface, that the Bath’s thermal water reaches between 64-96C, at about 2.5km down – this is based on the premise that the heat increases by about 20C for every kilometre of depth below the earth’s surface.

So, while it might sound more exciting to say so, saying that ‘volcanic-activity’ heats the water, doesn’t really do justice to the true nature behind the heat in Bath’s thermal springs!

This has a fairly simple answer which is – no!

As the water percolates through the rocks of the earth, it does pick up a multitude of different minerals, and over the years there have been various claims and stories about how the combination of these minerals can aid recovery of various ailments.  I suspect that mind-over-matter has a part to play in this, but many of these stories have perpetuated the idea that Bath’s springs are some kind of fountain of youth!

King Bladdud statue

Legendary founder of Bath, King Bladdud (alleged father of King Lear, of Shakespearean fame) and his herd of pigs both were allegedly cured of leprosy after bathing in the thermal water.  Whether or not Bladdud existed is the stuff of legend but if there is any truth in this story, there is a stronger possibility that the ailment in question was another epidemiological condition such as erysipelas which affects both humans and pigs and can look like the early onset of leprosy.  Can it be cured by bathing in hot, mineral-infused water?… probably not as it’s treated with antibiotics nowadays, but as this legend has been told for so long, there’s no telling what the truth could be… or is it just a good story!

Mary of Modena (wife and Queen Consort of King James II of England) became pregnant following a visit to Bath’s thermal springs.  The King had failed to father a son who survived infancy.  But when his wife gave birth to James Francis Stuart (eventually known as the ‘Old Pretender’ to the English throne), Bath’s springs suddenly got a reputation for curing ills!  Did bathing in Bath’s thermal water aid Mary of Modena in becoming pregnant?… I could say all sorts of things here though the likely answer is of course ‘no’… but again, there are hundreds of considerations we’ll never know the answer to.  At the time (late C17th) superstition fuelled social opinion, so there’s no wonder Bath’s thermal springs suddenly got so much attention following Mary’s visit!

There’s no question that bathing in our thermal waters feels nice and can have therapeutic effects, but the idea that drinking the water or bathing in it offers any cure, seems to be fantastical at best.  In fact, I’ve yet to find any verified medical or scientific suggestion that Bath’s thermal water has the power to do anything different to any other warm water!  In the 1970s a young girl tragically died after she swam in the water.  Subsequently, it was found that a meningitis causing bacteria had become resident in the geological fault through which the water reaches us.  Local environmental health officials monitor the water regularly, and I’ve been told this bacteria is still present in the water today.  Following the incident in the 1970s, the water was deemed inaccessible for some time until suitable filtration and safety measures could be put in place.  The spa bathing facilities remained closed for 40 years, until a new facility was built and opened in 2008.

Thankfully nowadays, the spa water you can drink when visiting the Roman Baths Museum or the Pump Room is heavily filtered between the source and the drinking fountains.  I’m told by staff in the local environmental services team, that the modern filtration process not only strips out the meningococcal bacteria but also removes some of the minerals the water has picked up during it’s journey from 2.5km down!… so if it ever did have health giving benefits in the past, those benefits would be somewhat different now.  Still… better safe than sorry, and it still feels nice when you swim in it!

There are many stories, facts, and figures about Bath’s hot springs and you can hear more anecdotal tales about them by joining one of our tours.  But there’s no question that without our famous springs, our beautiful city would not be as it is today!

Further reading on Bath’s springs:



To swim in Bath’s thermal waters visit:

https://www.thermaebathspa.com or


To drink the thermal waters you can do so by visiting:



Please bear in mind that the drinking fountains are occasionally unavailable for maintenance reasons, without advance notice.


  1. All opinions expressed are our own;
  2. While we do our best to validate and ensure facts & figures are correct, they are only as accurate as our sources claim.
If you have other questions you’d like to hear answers to about Bath’s famous thermal springs, please use the comments below!
Charles Gill
Charles Gill 1024 640 mike@savouringbath.com

A 5 min excerpt from one of our tours!… about a little known C18th character who influenced Bath’s culinary history and became something of a local celebrity during his time.