The Sacred Spring at the Roman Baths in Bath

Bath exists because of the emergence of three natural springs in the heart of the city which deliver over 1 million litres of mineral-rich water every day. Uniquely in the UK, the mineral water is hot - it rises to the surface at a constant temperature of at least 45° C.  These springs have been, and continue to be, at the centre of economic, social and cultural developments in the City. As such, their protection is of paramount importance locally and nationally.

Bath was, in fact, charged with responsibility for the Hot Springs in a Royal Charter of 1591 granted by Elizabeth I – this duty has passed to Bath & North East Somerset Council. The springs are further protected by the 1982 County of Avon Act.

Geology of Bath's Hot Springs

For further information on the geology of the hot springs you may be interested to read Dr Rameus Gallois' paper entitled The Geology of the Hot Springs at Bath Spa, Somerset. A link to the paper is on the right hand side of this page.

Mineralogy of Bath's Hot Springs

The analyses show that the thermal waters all contain sodium, calcium, chloride and sulphate ions in high concentrations.

The chemical composition of the spring waters has been examined over time. Although there are some small variations, in general, allowing for changes in analytical methods it has been concluded that composition has remained constant over the past century.

From: Kellaway, GA 1991



Expressed as

Concentration (Hetling Spring)

























Water Monitoring Systems

The temperature and flow and pressure of the springs has been monitored for many years by the local authority (firstly Bath City Council, and currently Bath and North East Somerset Council). The data is used for monitoring the potential impact on the Springs of any development within the City of Bath. The monitoring system also provides essential data for ongoing research into the origins of the Springs.

In addition to written reports, the water flow, pressure and temperature data is now gathered in a format appropriate for publishing on the Internet, so meeting the Council's desire to provide information in an accessible way to the public.

The information here is a summary report of monitoring data collected on behalf of B&NES with the technical assistance of Zenith International. The information is updated each month.


Explanatory Notes

The graphs can be viewed using the links on the right hand side of this page. They display flow, temperature and other physical properties of the water collected from the three Hot Springs in Bath. Namely the Kings spring, Hetling spring and Cross Spring. The data displayed is collected at 10-minute intervals by the data logging system located within the Roman Baths. The data shown for the Kings Spring is broken down into two components - The Kings (or Great) Bath and the Great Drain. The Stall Street borehole intercepts groundwater rising in the Kings Spring. The Hetling and Cross Springs are displayed separately.

The flow and temperature of the Hot Springs are known to be relatively constant.However, all of the data exhibits variations to a small degree. Most short-term changes in the recorded flows and temperatures are naturally occurring. Spring flows and temperatures also exhibit other variations. The main ones are described below:

  • The Stall Street Borehole shows frequent changes in flow and temperature. This occurs when flow to the Pump Room fountain is manually reduced or stopped, usually during concerts or other functions in the Pump Room.  
  • The Great Bath flow exhibits a slow decline with time. This happens because the pipework through which water flows to the Great Bath becomes coated with sediment from the springs. The overflow from the Kings Spring through the Great Drain shows a corresponding rise. The sum of the two flows is relatively constant as these constitute the total Kings Spring output. The flow to the Great Bath increases again whenever the pipework is cleaned.  
  • The temperatures of the Great Bath and Great Drain show variations due to daily and seasonal changes of ambient air temperature. Furthermore, if the flow rate reduces then so does temperature as the water has had more time to cool as it moves away from the spring.  
  • The Great Drain flow data exhibits "spikes" caused by rainfall. Rain also affects the temperature, pH and conductivity data recorded at some sites. Rainfall is measured and recorded so these "spikes" can be correlated with rainfall.

Other changes in the flow and temperature occur from time to time. Any significant variations are detailed and explained in the accompanying notes for each month's graphs.

MONTHLY DATA: Sept - Nov 2017

There are a few points in the data that require brief explanation and these are detailed below:

  • Kings Spring total flow under-reported throughout the period due to failure of Great Drain flowmeter. Flowmeter was replaced on 13/12/16 however new flowmeter is currently not recording correctly hence the data has been omitted from the flow charts.

  • The gradual decrease in flow through the Great Bath is as a consequence of pipe fouling..

  • The Hot Spring flowmeter is “noisy” due to electrical current fluctuations caused by the humid environment.

  • The Cross Bath Flow variations stem from manual flow adjustments made in response to a blocking drainage outlet.

  • The overall decrease in total flow is a consequence of manually reduced flow and the lack of reliable data from the Great Drain and Hot Spring flowmeters.

  • The temperature and pressure data demonstrates the overall stability of the Hot Springs system.

  • Periodic short term temperature decreases are associated with cleaning in place operations.

  • Gaps in the Great Bath Channel 1 temperature data are due to equipment failure.


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