Chemistry

Water's conductivity comes entirely from the tiny amount of H⁺ and OH⁻ ions it naturally produces through autoionization—so measuring conductivity lets you find their concentrations. The key is using the conductivity equation $\kappa = \lambda_m \times c$ (rearranged for individual ions) to back-calculate the ion concentrations from the measured $\kappa$ and known ionic conductances, then multiply those concentrations to get $K_w$.

Water's conductivity comes entirely from the tiny amount of H⁺ and OH⁻ ions it naturally produces through autoionization—so measuring conductivity lets you find their concentrations. The key is using the conductivity equation $\kappa = \lambda_m \times c$ (rearranged for individual ions) to back-calculate the ion concentrations from the measured $\kappa$ and known ionic conductances, then multiply those concentrations to get $K_w$.