It USED to be thought that the relatively warm equatorial spots were desiccated.
However, Mars Odyssey has shown quite large near equatorial areas have sizeable water fractions, perhaps up to 20%:

DPS 35th Meeting, 1-6 September 2003
Session 9. Mars Surface I
Oral, Chairs: E. R. Kraal and R. C. Quinn, Wednesday, September 3,
2003, 10:30am-12:00noon, DeAnza III
--------------------------------------------------------------------------------
[9.03] Mars Low-Latitude Neutron Distribution: Possible Remnant
Near-Surface Water Ice
B.M. Jakosky, M.T. Mellon, S. Varnes (Univ. of Colorado), W. Feldman
(LANL), W. Boynton (Univ. of Arizona), R.M. Haberle (NASA/Ames)

The Mars Odyssey GRS/NS has provided indications of near-surface water
in the equatorial and mid-latitudes, in amounts typically from 5-10 %
and ranging up to 15-20 %. Although such high abundances could be
present as adsorbed water in clays, other measurements suggest that
clays are not present. The spatial pattern of where the water is
located is not consistent with a dependence on composition (as would
be the case if it were related to clay), topography, present
atmospheric water abundance, latitude, or thermophysical properties.
The "wave-number two" pattern of water abundance is very reminiscent
of something related to an atmospheric phenomenon. We suggest that the
high water abundances could be due to transient ground ice that is
present in the top meter of the surface. Ice would be stable at
tens-of-centimeters depth at these latitudes if the atmospheric water
abundance were about twice the present value, much as ice is stable
poleward of about 60 degrees latitude for current water abundances.
Higher atmospheric water abundances could result under present-day
orbital conditions if the south-polar cap were to lose its annual
covering of CO2 ice; this would expose an underlying water-ice cap
that could supply water to the atmosphere during southern summer. If
this hypothesis is correct, then (i) the water ice is unstable today
and is in the process of sublimating and diffusing back into the
atmosphere, and (ii) the current configuration of perennial CO2 on the
south and not the north might not be representative of the present
epoch over the last ten thousand years.
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http://www.aas.org/publications/baas/v35n4/dps2003/52.htm

WATER-BEARING MINERALS ON MARS: SOURCE OF OBSERVED MID-LATITUDE WATER?
D. L. Bish, J. W. Carey, C. Fialips, Mineralogy & Geochemistry, Los Alamos
National Laboratory, Mail Stop D469, Los Alamos, NM 87545, b***@lanl.gov
Lunar and Planetary Science XXXIV (2003) 1786.pdf
http://www.lpi.usra.edu/meetings/lpsc2003/pdf/1786.pdf

CAN HYDROUS MINERALS ACCOUNT FOR THE OBSERVED MID-LATITUDE WATER ON
MARS?
D. L. Bish1,2, D. T. Vaniman2, C. Fialips2, J. W. Carey2, W. C.
Feldman2, 1Dept. of Geol. Sciences, Indiana University,
Bloomington, IN 47405, b***@indiana.edu; 2Los Alamos National Lab, MS
D469, Los Alamos, NM 87545.
Sixth International Conference on Mars (2003) 3066.pdf
http://www.lpi.usra.edu/meetings/sixthmars2003/pdf/3066.pdf

PROPERTIES OF POTENTIAL MARTIAN MINERALS UNDER SIMULATED SURFACE
CONDITIONS.
D. L. Bish1, D. T. Vaniman1, S. J. Chipera1, and J. W. Carey1,
1Hydrology, Geochemistry, and Geology, Los Alamos National Laboratory,
MS D469, Los Alamos, NM 87545 b***@lanl.gov.
Lunar and Planetary Science XXXIII (2002) 1895.pdf
"A better knowledge of Martian hydrous mineralogy,
measured under conditions representative of the
Martian surface, can provide answers to key questions
such as: (1) Can water deposits formed during early
Martian hydrologic cycles survive for time spans on the
order of hundreds of millions of years over which life
would form; (2) What is the difference in water retention
between polar and equatorial regoliths, and how
would these differences influence a search of Mars for
evidence of life; (3) What are the relationships between
permafrost and hydrous solids on Mars; and (4) Can
hydrous-mineral deposits in a brackish regolith provide
a water resource for human exploration and development of Mars?"
http://www.lpi.usra.edu/meetings/lpsc2002/pdf/1895.pdf

Bob Clark