The tunneling mechanisms in electrochemical STM are studied by distance and voltage tunneling spectroscopy in different model systems. The experimental results indicate an indirect tunneling process via intermediate states. Significant influences of the chemical nature and crystallographic orientation of the substrate and the structure of 2-D upd adlayers on the effective barrier height of the tunneling process are observed. The intermediate states are related to dipole resonances of well-ordered water dipoles located in the electrochemical double layers at the tip/electrolyte and substrate/electrolyte interfaces.