Numbers 19:7-8, 21

Then the priest shall wash his clothes and bathe his body in water; and afterward come into the camp, but he shall be [ceremonially] unclean until evening. The one who burns the heifer shall wash his clothes and bathe his body in water, and shall be unclean until evening.

So it shall be a perpetual statute to them. He who sprinkles the water for impurity [on another] shall wash his clothes, and he who touches the water for impurity shall be unclean until evening.