In this work we report the main conclusions of the European Space Agency (ESA) Metawave project (Mitigation of Electromagnetic Transmission errors induced by Atmospheric Water Vapour Effects) for what concerns the Synthetic Aperture Radar Interferometry (InSAR) viewpoint. The Atmospheric Phase Screen (APS) estimated with the Permanent Scatterers (PS) technique in the test sites of Roma and Como has been compared with MM5 simulations, Meris Water Vapor (WV) data and GPS Zenith Wet Delays (ZWD). The experiment shows that, even though MM5, Meris and GPS data detect the similar absolute amount of WV, their accuracy is not enough to compensate the InSAR sensitivity to the WV spatial variability. In particular, Numerical Weather Prediction models look promising for correcting long WV spatial wavelengths in presence of topography; GPS measurements reveal the best performances toward short WV spatial wavelengths, while Meris data in the analyzed area show generally poor reliability. © 2011 IEEE.