  Radiation-induced damage of biological matter is an ubiquitous problem in
nature. The influence of the hydration environment is widely discussed, but its
exact role remains elusive. Utilising well defined solvated-molecule
aggregates, we experimentally observed a hydrogen-bonded water molecule acting
as a radiation protection agent for ionised pyrrole, a prototypical aromatic
biomolecule. Pure samples of pyrrole and pyrrole(H$_2$O) were outer-valence
ionised and the subsequent damage and relaxation processes were studied. Bare
pyrrole ions fragmented through the breaking of C-C or N-C covalent bonds.
However, for pyrrole(H$_2$O)$^+$, we observed a strong protection of the
pyrrole ring through the dissociative release of neutral water or by
transferring an electron or proton across the hydrogen bond. Overall, a single
water molecule strongly reduces the fragmentation probability and thus the
persistent radiation damage of singly-ionised pyrrole.
