This image shows the Zone of Contribution (ZOC). This is the area needed to support an abstraction from long-term recharge (the proportion of the effective rainfall that infiltrates to the water table).

Pollutants arising and precipitation falling outside the boundary of the ZOC cannot flow to the well.

When considering issues relating to a well, such as protection, location of nearby potentially polluting developments, abstractions from other wells, etc., the main focus of attention is on the area delineated by the ZOC boundaries.