This dataset is from an array of tensiometers measuring soil water tension installed at the Llyn Hir monitoring site within the Pontbren study site in mid Wales, UK. Three tensiometers were installed at 10 cm, 30 cm, and 50 cm depth and sampled every 10 minutes between September 2008 to December 2009 as part of the Pontbren Catchment Study Land Use and Management Multi-Scale Experimental Programme. The Llyn Hir site is an area of unimproved grassland adjacent to the Llyn Hir rain gauge and Llyn Hir outflow stream gauging site (Site 8). Soil water tension data (cm H2O) are provided in the form of .txt files and generally split into 6 month blocks. Associated with each data point in the .txt file is a quality assurance code, QA code, in the adjacent column. Details of the dataset and the quality assurance coding system are provided in the supporting documentation. Datasets from the rain gauges and stream monitoring system at the Llyn Hir site are also provided by the EIDC.