  A decade ago, an electron-attachment process called interatomic Coulombic
electron capture has been predicted to be possible through energy transfer to a
nearby neighbor. It has been estimated to be competitive with
environment-independent photorecombination, but its general relevance has yet
to be established. Here, we evaluate the capability of alkali and alkaline
earth metal cations to capture a free electron by assistance from a nearby
water molecule. We introduce a characteristic distance $r_{IC}$ for this energy
transfer mechanism in equivalence to the F\"orster radius. Our results show
that water-assisted electron capture dominates over photorecombination beyond
the second hydration shell of each cation for electron energies above a
threshold. The assisted capture reaches distances equivalent to a fifth to
seventh solvation shell for the studied cations. The far reach of the assisted
electron capture is of significant general interest to the broad spectrum of
research fields dealing with low-energy electrons, in particular
radiation-induced damage of biomolecules. The here introduced distance measure
will enable quantification of the role of the environment for assisted electron
attachment.
