The adsorption kinetics of water on Ru(001) was simulated using molecular dynamics (MD) and equilibrium-model approach. The results nicely reproduce observations from STM imaging, work function change, and IR measurements. The agreement with experimental results is based on the formation of stable clusters already at very low surface coverage and temperature. Tetramers are predicted to be relatively stable compared to smaller and larger clusters. The dipole moment per water molecule continuously decreases from 2.2D for the monomer down to 1.1D for pentamer and larger clusters. Dimers are found to diffuse faster than monomers or larger clusters, with activation energy for diffusion of 2.9 kcal/mol, in agreement with recent STM measurements. A unique mechanism for dimers diffusion is proposed. Temperature programmed desorption (TPD) spectra from a metal surface were calculated by employing the MD scheme. These spectra were found identical to the standard Redhead line-shape analysis of the experimental TPD spectra of water from Pt(111) and Ru(001), an observation that was used to verify the consistency of the MD procedure. Finally, a kinetic model, fed by the MD calculated decreasing dipole moments per water molecule at larger clusters, explains well the highly nonlinear initial stages (up to 0.35BL) of the work function change data determined experimentally. (C) 2003 American Institute of Physics.