A private water supply is any supply of water intended for human consumption and not provided by the water undertaker appointed under Article 13 of The Water and Sewerage Services (Northern Ireland) Order 2006, i.e. NI Water Ltd. The Private Water Supplies Regulations (Northern Ireland) 2017 require the Drinking Water Inspectorate (DWI) to hold a register of private water supplies which includes supplies to public or commercial premises or two or more private dwellings where the water is used for drinking, cooking, food preparation or other domestic purposes. This spatial dataset (polygons) illustrates a layer of 100m by 100m squares, each of which is randomly described around a registered private water supply in Northern Ireland. Both private water supplies currently monitored, or historically monitored, by the Drinking Water Inspectorate are identifiable. This dataset was created on 30 December 2021 and superceded on 31 March 2022.