  This paper discusses the performance of electrical spectroscopy using a
RESPER probe to measure the salinity s and volumetric content {\theta}W of the
water in concrete or terrestrial soil. The RESPER probe is an induction device
for spectroscopy which performs simultaneous and non invasive measurements of
the electrical RESistivity 1/{\sigma} and relative dielectric PERmittivity
{\epsilon}r of a subjacent medium. Numerical simulations establish that the
RESPER can measure {\sigma} and {\epsilon} with inaccuracies below a predefined
limit (10%) up to the high frequency band (HF). Conductivity is related to
salinity and dielectric permittivity to volumetric water content using suitably
refined theoretical models which are consistent with the predictions of
Archie's and Topp's empirical laws. The better the agreement, the lower the
hygroscopic water content and the higher s; so closer agreement is found with
concrete containing almost no bonded water molecules provided these are
characterized by a high {\sigma}. A novelty of the present paper is the
application of a mathematical- physical model to the propagation of errors in
the measurements, based on a sensitivity functions tool. The inaccuracy of
salinity (water content) is the ratio (product) between the conductivity
(permittivity) inaccuracy, specified by the probe, and the sensitivity function
of salinity (water content) relative to conductivity (permittivity), derived
from the constitutive equations of the medium. The main result is the model's
prediction that the lower the inaccuracy for the measurements of s and
{\theta}W (decreasing by as much as an order of magnitude from 10% to 1%), the
higher {\sigma}; so the inaccuracy for soil is lower.
