The test experiment of a prototype water
Cherenkov detector consisting of six 8$B&U(B
photomultiplier tubes sunk in the reservoir pool of
21 m2 (7 m $B!_(B 3 m) and the depth
3 m was carried out at Mt. Norikura (2780 m a.s.l.) from 5 September to
3 October in 1994. The prototype detector detected showers
with frequency of about 40 Hz at the water depth 1.8 m.
For frequency data at several water depth,
we understand that the water depth 1.5 m , 2.0 m is
suitable for the water Cherenkov detector for observation of proton
initiated or gamma-ray initiated showers. The performance of the
prototype detector was simulated by a shower simulation code GEANT.
Results gotten by the simulation suggest that the prototype
detector detects mainly proton initiated air showers with
wide energy range from 10 GeV to 10 TeV.