  We describe here a new algorithm to model the water contents of the
atmosphere from GNSS slant wet delays relative to a single receiver. We first
make the assumption that the water vapor contents are mainly governed by a
scale height (exponential law), and secondly that the departures from this
decaying exponential can be mapped as a set of low degree 3D Zernike functions
(w.r.t. space) and Tchebyshev polynomials (w.r.t. time.) We give an example of
inversion with data acquired over a one day time span at the Geodesy
Observatory of Tahiti.
