  In this talk, we present the physics case for a megaton Water Cerenkov
detector in addressing some of the still pending questions in neutrino
oscillations physics, particularly the measurement of leptonic CP violation. We
compare different future beams that could profit from a water detector and
analyse, for the case $\theta_{13} \approx 3^\circ$ (the limit that can be
reached by under-construction experiments), the signal-to-background rate for a
$\beta$-beam setup with the radioactive ions accelerated to $\gamma = 350$.
