Numbers 19:1-10. God commands Moses and Aaron to bring a red heifer without defect and who has never born the yoke, to Eleazar, the priest. Eleazar is to is given strict instructions on how to sacrifice and burn the heifer and to use some of her blood to sprinkle on the front of the tent of meeting. Cedarwood, hyssop, and scarlet stuff are to be burnt with the sacrifice, then the ashes are to be gathered and deposited in a clean place outside the camp where they are to be kept for the congregation to use "for the water for impurity." The priest, the man who slaughters the heifer, and the one who gathers the ashes, are all to wash themselves and their clothes and shall be unclean until the evening. This is a permanent statute for Israel.

God goes to such great lengths to take care of his people! All of these explicit instructions, which are permanent statute to be done in every place or camp that the Israelites ever find themselves in, are meant to purify the tent of meeting and to have a constant supply of purified ashes available for the people to make the water for impurity, similar to our holy water of today. Clearly the water for impurity is vitally important for the holiness of the Israelites! 

This is God going to great lengths, and asking his priests to go to great lengths, to care for the everyday needs of his people in this fallen world. He loves us so much he looks to every detail of our lives and provides for us. It is truly amazing!