Drilling a private well for domestic use is generally exempted development and does not usually need planning permission on its own, though it is normally shown and assessed as part of a house's planning application where the house itself needs permission. Local restrictions, protected sites, or group water scheme areas can affect this, so it is worth checking with the local authority.
Drilling a well to supply water to a single private house is generally treated as exempted development under the Planning and Development Regulations 2001 (as amended), meaning a standalone application specifically for the well is not usually required. In practice, however, a well is rarely drilled in isolation — it is almost always part of a proposal to build or extend a house that does need planning permission, and in that context the well's location, expected yield, and separation distance from any septic tank or wastewater treatment area on the site (and on neighbouring land) will be assessed by the planning authority as part of that application.
This matters because the safe siting of a well relative to sources of contamination is central to whether a rural house on a private water supply will be granted permission, so even though drilling itself may be exempt, the planning process still controls where a well can go. Certain locations may also carry additional constraints, for example within a groundwater source protection zone, a Special Area of Conservation, or where the site is served by a group water scheme with its own connection rules rather than a private well being appropriate.
Because exemptions can be affected by local conditions, cumulative development, or specific area designations, it is sensible to confirm the position with the local authority's planning section before drilling, particularly if the well is not part of a wider planning application already before the council.