Buried water services have at least the minimum cover set in the standard's cover table, measured from finished surface level and varying with location and loading (under slabs, non-trafficked ground, fire services, vehicle loads by carriageway type, embankments) (2003 text; the current figures are in the 2021 table).
The graph holds this control, the 0 it maps to, and the evidence behind each claim, over MCP and REST.