The same way every hydroponic system saves water. Recirculation.
Traditional soil growing literally pours the water on the ground, where most of it evaporates, and what doesn’t sinks into the soil and becomes unrecoverable on any reasonable timescale.
Traditional soil growing literally pours the water on the ground, where most of it evaporates, and what doesn’t sinks into the soil and becomes unrecoverable on any reasonable timescale.