A sacrifice was required to produce the water of purification. More details are given here for who is clean and who is uncleaned.

Numbers 19

The LORD spoke to Moses and Aaron, saying:

2 “This is the ordinance of the law which the LORD has commanded, saying ‘Speak to the children of Israel, and tell them to bring you a red heifer without spot or blemish, which has never been yoked:

3 And you shall give her to Eleazar the priest to take her outside of the camp, and one shall slay her before his face:

4 Eleazar the priest shall take some of her blood with his finger, and sprinkle some of her blood directly before the tent of meeting seven times:

5 The heifer shall be burned in his sight; her skin, and her flesh, and her blood, with her dung, shall be burned. 

6 And the priest shall take cedar wood, and hyssop, and scarlet, and cast it into the midst of the fire where the heifer is burning. 

7 Then the priest shall wash his clothes, and bathe his body in water, and afterward he shall come into the camp, and the priest shall be unclean until evening.

8 The person who burns the heifer shall wash his clothes in water, and bathe his body in water, and shall be unclean until evening.

9 A man that is clean shall gather up the ashes of the heifer and deposit them outside the camp in a clean place, and they shall be kept for the congregation of the children of Israel for the water of separation: it is a purification for sin.

10 The one who gathers the ashes of the heifer shall wash his clothes and be unclean until evening: and it shall be to the children of Israel, and to the stranger that lives among them, for a statute forever.

11 Whoever touches the dead body of any man shall be unclean for seven days. 

12 He shall purify himself with it on the third day, and on the seventh day he shall be clean: but if he does not purify himself on the third day, then on the seventh day he shall not be clean.

13 Whoever touches the dead body of any man that is dead, and does not purify himself, defiles the tabernacle of the LORD; and that soul shall be cut off from Israel: because the water of separation was not sprinkled on him, he shall be unclean; his uncleanness stays on him.

14 This is the law, when a man dies in a tent: all that come into the tent, and all that is in the tent, shall be unclean for seven days.

15 Every open vessel, which has no covering on it, is unclean.

16 Whoever touches one that is slain with a sword in the open fields, or a dead body, or a bone of a man, or a grave, shall be unclean for seven days.

17 An unclean person shall take some of the ashes of the burnt heifer of purification for sin, and place them in a vessel with fresh water. 

18 And a clean person shall take hyssop, and dip it in the water, and sprinkle it on the tent, and on all the vessels, and on the people that were there, and on theone that touched a bone, or one slain, or one dead, or a grave:

19 The clean person shall sprinkle the unclean on the third day, and on the seventh day: and on the seventh day he shall purify himself, and wash his clothes, and bathe himself in water, and shall be clean at evening.

20 But the man that is unclean, and does not purify himself, that person shall be cut off from among the congregation, because he has defiled the sanctuary of the LORD: the water of separation has not been sprinkled on him; he is unclean.

21 It shall be a perpetual statute to them, that he who sprinkles the water of separation shall wash his clothes; and he that touches the water of separation shall be unclean until evening.

22 Anything the unclean person touches shall be unclean; and the person that touches it shall be unclean until evening.

See also: Numbers 19 in ESV, HCSB, NASB and NIV via Bible Gateway.