Synchrotron radiation in the energy range between 6 and 30 eV was used to study the photon‐stimulated field desorption (PSFD) from a water covered Ag‐field emitter. Above a threshold energy of 7.4 eV (extrapolated for zero electric field) a variety of protonated water clusters (H2O)n⋅H+,n=1,...,15, are observed. The influence of the surface temperature, electric field, photon energy, and photon flux on the PSFD spectra are measured. Under certain experimental conditions the predominance of themagicclusterion(H2O)4⋅H+is observed.