Warimizu means adding water, to be more precise, shuzo yosui to sake, that was taken out of the storage tank used for storing and maturing, immediately before shipment.
割水（わりみず）とは、貯蔵・熟成のための貯蔵タンクから出された酒へ、出荷の直前に水を、より正確には酒造用水を加える作業をいう。