  We present a sample of eight cataclysmic variables (CVs) identified among the
X-ray sources of the 400 square degree (400d) X-ray ROSAT/PSPC survey. Based on
this sample, we have obtained preliminary constraints on the X-ray luminosity
function of CVs in the solar neighbourhood in the range of low luminosities,
L_X=~1e29-1e30 erg/s (0.5-2 keV). We show that the logarithmic slope of the CV
luminosity function in this luminosity range is less steep than that at
L_X>1e31 erg/s. Our results show that of order of thousand CVs will be detected
in the SRG/eROSITA all-sky survey at high Galactic latitudes, which will allow
to obtain much more accurate measurements of their X-ray luminosity function.
