We explore the spatiotemporal evolution of dispersion-induced pulse broadening in water. The Lorentz–Lorenz function is utilized to establish the relationship between the refractive index and the wavelength of the incident laser. Therefore, the dispersion coefficients are derived. Using the Schrödinger equation, we model the propagation of laser pulses over a 1-m optical length in water. Subsequently, the spatiotemporal evolution is obtained by the relationship between the spatial and temporal components of the light field. The results indicate that lasers with shorter central wavelengths and shorter pulse durations experience greater pulse broadening and significant bandwidth reduction. This methodology demonstrates the potential for enhancing underwater optical communication, representing a noteworthy advancement in both scientific research and practical applications.