A liquid treatment method according to an aspect of the present disclosure comprises: starting application of a power between a pair of electrodes to generate plasma, which causes active species to be produced in a liquid； measuring the hydrogen ion concentration in the liquid while the plasma is generated； measuring a time elapsed after the starting the application of the power； and stopping the application of the power when a value calculated by (a) multiplying the hydrogen ion concentration by the elapsed time or (b) integrating the hydrogen ion concentration with respect to the elapsed time is larger than a first threshold.
