A to Z Index

Bath - Hot Springs

Protection and Water Monitoring

To view Hot Springs Temperature Data Graph

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.

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

Mineral	Expressed as	Concentration (Hetling Spring)
Sodium	mg/l	195
Calcium	mg/l	358
Sulphate	mg/l	1015
Chloride	mg/l	340
Bicarbonate	mg/l	193
Magnesium	mg/l	57
Silicon	mg/l	21
Iron	mg/l	0.5

Water Monitoring Systems

The temperature and flow 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 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.

Zenith International is based in Kingsmead Square, Bath - little more than a stone's throw from the hot springs. The Water & Environment group is one of the UK's leading teams of hydrogeologists with expertise in a whole range of groundwater and water resources projects. Their experience with the hot springs dates back to 1998 when they reviewed the old monitoring system, leading to recommendations for a much-improved and more reliable replacement. They then managed the procurement and installation of the new system and have since provided monitoring services and advice to Bath & North East Somerset Council over a number of years.

Explanatory Notes

The graphs above 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: August 2008

The data for February 2008 is now available by following the links to the graphs above.

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

Gradual increase in Great Drain flow throughout the most of the month in response to a decrease in flow through GB2
Apparent fluctuations in Great Drain flow from 31/08/08; possibly due to sensor error
Incorrect Hetling Borehole temperature data recorded throughout the month – has been removed from the graph to allow clear presentation of other temperatures
Small fluctuations in Cross Bath temperature throughout the month thought to be cause by sensor error
Great Drain temperature sensor error from 30/08/08 – no temperature recorded from this date
Stall Street Fountain flow switched off overnight on 30/08/08. Corresponding apparent decrease in temperature
Temperature recorded at the Great Drain, and to a lesser extent GB2, decreases in response to heavy rain events
Apparent fluctuations in Hetling Borehole pressure recorded throughout the month; most likely due to sensor error. Currently under investigation
Minor variations in flow, temperature and pressure at Hetling Borehole, Cross Bath and Stall Street Borehole are due to Spa cleaning in place programmes and regular water sampling