Water has long served as a recipient of human confession across cultures. We present \textit{Whispering Water}, an interactive installation that materializes human-AI dialogue through cymatic patterns on water. Participants confess to a water surface, triggering a four-phase ritual: confession, contemplation, response, and release. Speech sentiment is translated into excitation frequencies that prime the water's physical state, while semantic content enters a multi-agent system of heterogeneous LLMs whose identities emerge through situated discourse. A novel algorithm decomposes synthesized speech into harmonic components via logarithmic spacing and Bark-scale mapping, reconstructing machine voices as physical wave superpositions. The installation explores emotional self-exploration through sensory-rich, ritually framed human-AI interaction.