World-wide distribution of main hydrogeological units

About 35% of the area of the continents (excluding the Antarctic) is underlain by relatively homogeneous aquifers, 18% is endowed with groundwater, some of which are extensive, in geologically complex regions. Nearly half of the continental areas (47%) contain generally minor occurrences of groundwater that are restricted to the near-surface unconsolidated rocks, where groundwater resources are usually sufficient for small to medium-sized population centres. Source: BGR & UNESCO