Rashi on Leviticus 11:32/רש"י על ויקרא י״א:ל״ב

1במים יובא IT MUST BE PUT INTO WATER — but even after it has been immersed, טמא IT IS UNCLEAN in respect to using it to hold the heave - offering,

2עד הערב UNTIL THE EVENING, AND — afterwards — וטהר IT BECOMETH CLEAN at the setting of the sun (Yevamot 75a).