The novel idea of water Cherenkov calorimeter made of water tanks as the next generation neutrino detector for nu factories and nu beams is investigated. A water tank prototype with a dimension of 1*1*13m^3 is constructed, its performance is studied and compared with a GEANT4 based Monte Carlo simulation. By using measured parameters of the water tank, including the light collection efficiency, attenuation length, angular dependent response etc, a detailed Monte Carlo simulation demonstrates that the detector performance is excellent for identifying neutrino charged current events while rejecting neutral current and wrong-flavor backgrounds.

The water tank prototype with a dimension of 1m x 1m x 13m was constructed as a building block of the Cerenkov calorimeter for very long baseline neutrino oscillation experiments. The effective attenuation length of the water tank was measured to be (5.74 +/- 0.29)m, and the light collection probability as a function of the incident angle of the particle is studied. Results are compared with a Monte Carlo simulation based on GEANT4 package which incorporates detailed optical processes. A good agreement is achieved and the water tank is feasible for the construction of the Cerenkov calorimeter.