An ADU proposal may raise a groundwater question if it includes a septic-tank soakaway, another discharge to ground, or work that could create a pollution pathway. In England, the Environment Agency’s Source Protection Zones (SPZs) are a screening map around groundwater abstractions used for domestic supply or food production. The map helps identify a check; it does not decide an individual proposal’s permit route.
Find the zone and its map source
Use the Environment Agency’s current guidance to open the SPZ layer in the MAGIC map or the related Defra data service. Search by postcode or parcel context, then record the map date and the boundary shown. The zones are modelled from groundwater travel time and other abstraction criteria; they are not simply uniform circles around every private well.
The guidance describes four main zone types:
| Zone | What the guidance describes |
|---|---|
| SPZ1 | The inner zone: the largest of the area within 50 metres of an abstraction point or the area from which groundwater reaches it within 50 days. |
| SPZ2 | The outer zone: a distance based on the permitted abstraction volume, or an area with a groundwater travel time of up to 400 days; the largest applicable area is used. |
| SPZ3 | The total catchment area from which groundwater reaches the abstraction point. |
| SPZ4 | An additional zone used where local conditions require special protection. It is not present everywhere. |
Some mapped zones extend beneath protective geology, such as clay, where deep drilling could create a path for pollutants. Check the map legend and current guidance rather than inferring a zone from a distance alone.
Ask what the proposal changes
If a parcel appears to intersect a zone, describe the actual work to the Environment Agency and local planning authority. Explain the proposed drainage or discharge method, groundworks, and any relevant well, borehole, or spring. Ask whether the activity has a pollution pathway, which environmental permit or pollution-prevention rules apply, and what supporting information is needed.
A zone does not prove that an ADU is unsuitable or that a permit is automatically required. Conversely, no visible zone does not establish that every discharge or environmental requirement is clear. Mains drainage, private drainage, planning permission, building approval, and environmental permits are separate checks. Use the wider site-constraint screening sequence and confirm the current route with the responsible authority.
This page applies to England. Wales, Scotland, and Northern Ireland have separate environmental authorities and mapping systems. It does not determine the location of a groundwater source, the pollution risk from a specific design, or whether a particular ADU needs permission.