<p>A nonlinear rate-equation formulation of nanosecond laser-induced breakdown in water-like media is developed, with polarization ellipticity introduced as a continuous symmetry parameter of the driving field. The rotational structure of the excitation is embedded directly into the governing equation for the free-electron density, enabling a systematic examination of avalanche ionization dynamics. A closed-form analytical solution of the nonlinear evolution equation is derived and its predictions are compared with independent numerical calculations. The results demonstrate that symmetry enters the governing amplification structure of the system, modifying the effective growth mechanism that controls plasma formation. To characterize this dependence in a compact and physically transparent manner, two global measures are introduced: the suppression factor of the peak electron density and the characteristic delay time of breakdown onset. The proposed formulation provides a mathematically consistent framework for analysing symmetry-controlled ionization processes in the nanosecond regime and supports modelling of laser-matter interaction in condensed media relevant to biomedical and engineering applications.</p>