Category 603
Additional exposuresLocal environment ⏵ Water minerals


Water hardness classifications are provided based on United States Geological Survey and World Health Organization definitions of domestic water calcium carbonate concentration. The results were obtained from freedom of information requests to local water supply companies across England, Scotland, and Wales. Postcodes were assigned to participant-visit instances based on approximate location (rounded to nearest km) and the assigned postcodes were used as a link to surveyed locations.

Data for baseline visits were derived from survey results for 2005. Data for repeat assessment and imaging visits were derived from survey results from 2013. The survey year for a particular result has been provided as a separate instanced data field, and can be used as an additional QC variable.

For measures relating to non-baseline visits - First repeat assessment visit (2012-13), or Imaging visit (2014+) - in most cases the address used to map to the water hardness surveys was from a single visit (either instance 1, or instance 2). For approximately 5,900 cases where a partipant had both instance 1 and instance 2 visits, and additionally did not move address between these visits, the results have been assigned to their repeat assessment visit (instance 1).

Data in this category were provided by the University of Melbourne. Methods used to derive these results are outlined in:

Lopez DJ, Singh A, Waidyatillake NT, Su JC, Bui DS, Dharmage SC, Lodge CJ, Lowe AJ. The association between domestic hard water and eczema in adults from the UK Biobank cohort study. Br J Dermatol. 2022 Nov;187(5):704-712. doi: