THE NAME
It started in Belgium
Spa, a town in the Ardennes, was so famous for its mineral springs that its name was given to resorts like it everywhere.
Read the factsTHERMAL SPRINGS, EXPLAINED
Rain in.
Hot water out.
Every spa town starts with a spring, and every hot spring starts as rain.
Compare spring temperatures
SPRINGfed, not heated
- Rain soaks in
- Rock heats it
- A spring returns it
- A town grows round it
The word spa comes from one small Belgian town. The hot water in towns such as Bath is old rainwater that sank kilometres into the rock and came back up warm. Here is how it works, in plain English.
Plain English, with the sources linked.
Updated
THE SHORT ANSWER
A name, a heat, a town.
Three things explain almost every spa town:
where the word came from, why the water is warm, and what grew around it.
THE HEAT
Deep rock, not a boiler
Rain sinks kilometres underground, warms up in the hot rock and rises again through cracks and fissures.
See two springs
THE TOWNS
Eleven on one list
UNESCO lists eleven spa towns in seven countries as one World Heritage property, Bath among them.
Compare the springsA QUICK SPRING CHECK
How warm is
the water?
Pick a water source to see how warm it is when it reaches the surface. The figures come from the British Geological Survey, the Geological Society and the Czech tourist board.
These are temperatures at the spring itself, as the sources give them, not the temperature of any pool or bath.
TWO SPRINGS WORTH KNOWING
Steady flow,
serious heat.
Two of Europe’s best-known spa towns,
side by side.
1.3 million litres
Water from the springs every day
Rain falls on the Mendip Hills south of Bath and seeps into the Carboniferous Limestone. It reaches about 2.5 km down, picks up heat, and emerges in the city at around 40 to 47 °C.
BATH · ENGLAND
2,000 litres a minute
Flow of the Vřídlo hot spring
The Vřídlo is the hottest spring in this guide at 72 °C. Its jet of water can reach up to 12 metres, and it is the town’s only thermal source used for bathing.
KARLOVY VARY · CZECHIA
Both towns are part of the Great Spa Towns of Europe, inscribed by UNESCO in 2021. All eleven towns developed around natural mineral water springs.
VISITING A SPA TOWN
Four ways
to read a spa town.
Find the spring first
Every one of the eleven UNESCO spa towns grew around natural mineral springs. Start with the spring, then see how the streets and buildings gather round it.
Learn the local word
In Spa the springs are called pouhons. Local names are often the quickest way into a town’s history.
Compare it with ordinary water
UK groundwater is about 10 to 12 °C. The warmer a spring is, the deeper its water has probably travelled.
Use only marked pools and fountains
Spring water can be very hot at source and is mineral-rich. Bathe and drink only where the town or spa says it is meant for visitors.
SPRING FACTS
Five things worth
knowing.
The word is a place name
Merriam-Webster traces spa to Spa, a watering place in Belgium, and dates its first known use in English to 1610.
Spa’s springs were rediscovered in 1326
Britannica notes they were known in Roman times and mentioned by Pliny the Elder, then rediscovered in 1326 and visited by European royalty in the 18th century.
About 26 °C warmer per kilometre
Rock temperature rises by about 26 °C for every kilometre of depth, though the rate varies with the rock. That is why deep-circulating water comes back warm.
Bath’s water may be thousands of years old
Estimates collected by the British Geological Survey range from a few hundred or thousand years up to 6,000 to 8,000 years. The true age is still uncertain.
A golden age from about 1700 to the 1930s
UNESCO says the European spa phenomenon has roots in antiquity, but reached its highest expression from around 1700 to the 1930s.
QUICK QUESTIONS
Spas, answered.
Short answers to the questions people ask most.
Where does the word spa come from?
From Spa, a town in the Ardennes of eastern Belgium, south-east of Liège. Its mineral springs, known locally as pouhons, became so well known that the name was given to health resorts of this kind in general. Merriam-Webster dates the first known use in English to 1610.
Why is the water in a hot spring warm?
Rock gets warmer with depth. Around Bath, rain soaks into limestone, sinks to about 2.5 km and is heated by the surrounding rock, at a typical rate of about 26 °C per kilometre, before rising back up through fissures.
How hot are the springs in Bath?
The British Geological Survey lists the three principal springs at about 45 °C (King’s Spring), 41 °C (Cross Bath) and 47 °C (Old Royal Spring). Ordinary UK groundwater is about 10 to 12 °C.
What are the Great Spa Towns of Europe?
A UNESCO World Heritage property inscribed in 2021: eleven towns in seven countries, including Bath, Spa, Vichy, Baden-Baden and Karlovy Vary. All grew up around natural mineral springs, and the spa culture they share peaked from around 1700 to the 1930s.
How old is the water that comes out of a hot spring?
It varies and is hard to pin down. For Bath, the British Geological Survey reports estimates ranging from a few hundred or thousand years up to 6,000 to 8,000 years, and notes that the age and depth remain uncertain.
Where the facts come from
- The Great Spa Towns of Europe (inscribed 2021)UNESCO World Heritage Centre
- Spa, Belgium: the town and its springsEncyclopaedia Britannica
- Spa: definition and etymologyMerriam-Webster
- Geosites: the hot springs of BathThe Geological Society
- Water supply and hot springs, Bristol and Gloucester regionBritish Geological Survey
- Carlsbad: the Vřídlo thermal springVisitCzechia