During the high densities of a supernova core collapse, some of the neutrinos provide the pulse to starts the outward moving shock wave. But most of the neutrinos zip out of the supernova core. Thus, when a supernova explodes, huge numbers of neutrinos pour into space, streaming across the Galaxy passing through dust, gas, nebula unhindered. Even if the supernova is obscured, the neutrinos will rain down on the Earth. However, because neutrinos are weakly interacting, they are also just as difficult to detect.
Water contains lots of protons in the form of hydrogen atoms.
Neutrinos from a supernova explosion travel at or very near the speed of light and carry a lot of energy. This collision will produce a positron which recoils with such high speed that it emits a brief flash of light known as Cerenkov radiation . The detector tank of water is buried deep in the Earth to eliminate cosmic rays and other interactions that would distort the detection of the neutrinos. Only neutrinos can reach to such depths. Twelve neutrinos were detected 3 hours after the supernova was seen in the optical.