And again, context is your key to understanding the Scriptures.
8It happened when Elisha the man of God heard that the king of Israel had torn his clothes, that he sent word to the king, saying, “Why have you torn your clothes? Now let him come to me, and he shall know that there is a prophet in Israel.” 9So Naaman came with his horses and his chariots and stood at the doorway of the house of Elisha. 10Elisha sent a messenger to him, saying, “Go and wash in the Jordan seven times, and your flesh will be restored to you and you will be clean.”
11But Naaman was furious and went away and said, “Behold, I thought, ‘He will surely come out to me and stand and call on the name of the LORD his God, and wave his hand over the place and cure the leper.’ 12“Are not Abanah and Pharpar, the rivers of Damascus, better than all the waters of Israel? Could I not wash in them and be clean?” So he turned and went away in a rage.
13Then his servants came near and spoke to him and said, “My father, had the prophet told you to do some great thing, would you not have done it? How much more then, when he says to you, ‘Wash, and be clean’?” 14So he went down and dipped himself seven times in the Jordan, according to the word of the man of God; and his flesh was restored like the flesh of a little child and he was clean.
15When he returned to the man of God with all his company, and came and stood before him, he said, “Behold now, I know that there is no God in all the earth, but in Israel; so please take a present from your servant now.” 16But he said, “As the LORD lives, before whom I stand, I will take nothing.” And he urged him to take it, but he refused. 17Naaman said, “If not, please let your servant at least be given two mules’ load of earth; for your servant will no longer offer burnt offering nor will he sacrifice to other gods, but to the LORD. 18“In this matter may the LORD pardon your servant: when my master goes into the house of Rimmon to worship there, and he leans on my hand and I bow myself in the house of Rimmon, when I bow myself in the house of Rimmon, the LORD pardon your servant in this matter.” 19He said to him, “Go in peace.” So he departed from him some distance. 2 Kings 5:8-19 NASB
It is the belief of the man of God that is what healed Naaman....not the water.
He was obedient to Elisha...the man of God.
And what was the overall purpose of this encounter?
15When he returned to the man of God with all his company, and came and stood before him, he said,
“Behold now, I know that there is no God in all the earth, but in Israel; so please take a present from your servant now.” 2 Kings 5:15 NASB
What we see in the NT with the Apostles are direct healings of people and the casting out of demons.....no "holy water" required....and why....because they are doing so through the name of Jesus Christ.
Again....if the Roman Catholic wants to live under the OT LAW they have to subject themselves to all of it.
Nobody's denying that this miracle of healing water helps attach Naaman to Israel and Israel's God, and that the healing is done by the power of God.
But you're not comprehending another point here: that God uses secondary causes. This is normal for God. This is the way He goes about working through His creatures: blessed bread, blessed wine, blessed oil, a blessed staff for Aaron, blessed cloths touched by Paul, blessed waters of Siloam, waters of the Jordan, the Pharaoh's-Army-destroying waters of the Red Sea, waters flowing from the right side of the Temple, the sin-destroying waters of the Great Flood, the breathed-upon waters throughout the Bible, the soul-cleansing blood and water from the pierced heart of the Crucified One.
Here are commentaries on God's blessing of the Waters, by eminent Protestant teachers (Ellicott's Commentary, Cambridge Commentary, the Keil and Delitzsch Biblical Commentary; MacLaren's Expositions; Benson Commentary; Jamieson-Fausset-Brown Bible Commentary; Gill's Exposition of the Entire Bible). These make reference to the healing miraculous waters in Ezekiel 47, and every one one of them comments on how God repeatedly and strikingly uses water to manifest His will and His healing and purifying power.
It is so plain I don't know how it could be plainer.
This is our prayer and faith seeing God's work in the use of His creature, water.
We use holy water through faith in God's (!) power. You could too, if you had this faith. GOD DOES NOT CHANGE.