  We discuss the potential of detecting thermal neutrinos from matter-rich
binary mergers, via a decades-long multi-messenger campaign involving a
Mt-scale water Cherenkov neutrino detector and one or more next generation
gravitational wave detectors, capable of observing mergers up to redshift
$z\sim 2$. The search of neutrinos in time-coincidence with gravitational wave
detections will allow to identify single neutrinos from individual mergers
above the background, and to study their distributions in energy, redshift and
type (double neutron-star or neutron-star-black hole merger) of the candidate
sources. We find that, for merger rates consistent with current LIGO-Virgo
constraints, and for a $100~{\rm Mt\cdot yr}$ exposure, between ${\mathcal
O(10^{-1})}$ and ${\mathcal O(10)}$ neutrino events are expected. For extreme
cases of mergers with more than $10^{52}$ ergs emitted in $\mathrel{{\bar
\nu}_e}$, the number of events can be as large as $\sim 100$, with sensitivity
to mergers up to redshift $z\sim 0.5$ or so. Such scenarios can already be
tested with a $10~{\rm Mt\cdot yr}$ exposure, resulting in constraints on the
post-merger evolution of the systems being considered.
