Water, air, and some other similar medias are usually used to generate Cherenkov light, which
are crucial for detecting high-energy rays or particles. Because of the quality of the media, the
contaminants will observe the Cherenkov light, resulting in the error reconstruction of the rays
or particles. Here we employed a method, similar to the integrating ring-down spectroscopy for
evaluating the water quality. This method induced the laser as light source, PMT as a detector
to record the decay signal, and the bucket with high reffective diffused material in the inner wall
to reffect the light. We choose copper sulfate solution to ffnd the relationship between solution
concentration, the attenuation length of water, and the reffectivity of inner-wall material. The
results proved the feasibility of the reffection cavity. This method can also be applied on the
monitor of atmosphere, water pollution and cave safety, etc.