Groundwater temperature data from a shallow urban aquifer in Cardiff, Wales, UK between 2014-2018. Monitoring was undertaken as part of the ‘Cardiff Urban Geo-Observatory’ project . Boreholes are located within the urban area of the City of Cardiff, Wales, UK. The majority of temperature sensors were installed within boreholes that monitor a shallow Quaternary aged sand and gravel aquifer, however the made ground and the Triassic Mercia Mudstone also represented. Temperature sensors installed in 53 boreholes, between depths of 1.5m and 12- m below ground, with measurements every 30 minutes. The dataset comprises of just over 3.5 million temperature measurements. Monitoring was undertaken by the British Geological Survey and was designed to address knowledge gaps of subsurface urban heat island and it use for heat recovery and storage. Metadata Report http://nora.nerc.ac.uk/id/eprint/525332/