One who has become impure through contact with a corpse is purified by sprinkling him on the third and seventh days with water in which the ashes of a red cow have been mixed, as it says "They shall take an unblemished red cow... and they shall take for the impure person some of [its] ashes and put on it living water in a vessel; and a pure man shall take hyssop and dip it in the water... and sprinkle on the impure person on the third day and on the seventh day... and he shall wash in water and be clean in the evening".¹ Those who slaughter the cow and prepare the ashes become impure for a day,² as do those who burn the sin-offerings that are not eaten and who take the scapegoat to the desert.³ One who touches or moves the water before it has been sprinkled, except to sprinkle it, also becomes impure for a day, as it says "And one who sprinkles the water of isolation shall wash his clothes, and one who touches the water of isolation shall be impure until evening".^4,a

Sources:
1. Num. 19:2-19	a. 5:1,4; 11:1; 15:1
2. Num. 19:7-8,10
3. Lev. 16:26,28
4. Num. 19:21