These laws will never change. The man who sprinkled the water and the ashes on you when you were unclean must also wash his clothes. And whoever touches this water is unclean until evening.
After the ceremony, the priest is to take a bath and wash his clothes. Only then can he go back into the camp, but he remains unclean and unfit for worship until evening.
A man who isn't unclean must collect the ashes of the burnt cow and store them outside the camp in a clean place. The people of Israel can mix these ashes with the water used in the ceremony to wash away sin.