John 3:22 After these things came Jesus and his disciples into the land of Judaea; and there he tarried with them, and baptized. 3:23 And John also was baptizing in Aenon near to Salim, because there was much water there: and they came, and were baptized. 3:24 For John was not yet cast into prison. 3:25 Then there arose a question between some of John's disciples and the Jews about purifying.
Verse 25 describes this "be baptized... wash away thy sins," and it does so in relation to verse 23's "water."
Of this water baptism as a symbolic washing away of sins under the Law, Peter would later write the following to the Israel of God (he was not writing to the Body of Christ)....
1 Peter 3:20 Which sometime were disobedient, when once the longsuffering of God waited in the days of Noah, while the ark was a preparing, wherein few, that is, eight souls were saved by water. 3:21 The like figure whereunto even baptism doth also now save us (not the putting away of the filth of the flesh, but the answer of a good conscience toward God,) by the resurrection of Jesus Christ:
The answer of an Israelite's good conscience toward God?
Luke 7:29 And all the people that heard him, and the publicans, justified God, being baptized with the baptism of John. 7:30 But the Pharisees and lawyers rejected the counsel of God against themselves, being not baptized of him.
What was going on in Acts 9 is that although Paul was already saved - by the Lord's evangelizing him Himself - the Lord then had Ananias go to Paul, etc, that Paul might later be able to point to "one Ananias, a devout man according to the law, having a good report of all the Jews which dwelt there..." as a witness the devoutness of which under the Law, many Jews at Damascus were familiar with.
But Paul was now among his own, there at Damascus, and the Israelite practice of symbolic putting away of the sins of the flesh through their water ritual under the Law, was a practice of Israelites.
Note Paul's submitting to that when in their company, once more...
Acts 21:22 What is it therefore? the multitude must needs come together: for they will hear that thou art come. 21:23 Do therefore this that we say to thee: We have four men which have a vow on them; 21:24 Them take, and purify thyself with them, and be at charges with them, that they may shave their heads: and all may know that those things, whereof they were informed concerning thee, are nothing; but that thou thyself also walkest orderly, and keepest the law.
Acts 21:26 Then Paul took the men, and the next day purifying himself with them entered into the temple, to signify the accomplishment of the days of purification, until that an offering should be offered for every one of them.
Notice the purification is prior to his entering the Temple.
One aspect of that of which were issues such as...
Exodus 30:17 And the LORD spake unto Moses, saying, 30:18 Thou shalt also make a laver of brass, and his foot also of brass, to wash withal: and thou shalt put it between the tabernacle of the congregation and the altar, and thou shalt put water therein. 30:19 For Aaron and his sons shall wash their hands and their feet thereat: 30:20 When they go into the tabernacle of the congregation, they shall wash with water, that they die not; or when they come near to the altar to minister, to burn offering made by fire unto the LORD: 30:21 So they shall wash their hands and their feet, that they die not: and it shall be a statute for ever to them, even to him and to his seed throughout their generations.
Things like...John 2:6 And there were set there six waterpots of stone, after the manner of the purifying of the Jews, containing two or three firkins apiece.
Most (not all) of which the writer of Hebrews describes to his fellow Hebrews were rituals...
Hebrews 9:10 Which stood only in meats and drinks, and divers washings, and carnal ordinances, imposed on them until the time of reformation.
Here is a water baptism....
Leviticus 11:35 And every thing whereupon any part of their carcase falleth shall be unclean; whether it be oven, or ranges for pots, they shall be broken down: for they are unclean, and shall be unclean unto you. 11:36 Nevertheless a fountain or pit, wherein there is plenty of water, shall be clean: but that which toucheth their carcase shall be unclean.
That is just like this one...
John 3:23 And John also was baptizing in Aenon near to Salim, because there was much water there: and they came, and were baptized.
Though, as the Lord revealed to Peter - after Paul was saved by the Lord on the road to Damascus absent of any ritual...
Acts 15:7 And when there had been much disputing, Peter rose up, and said unto them, Men and brethren, ye know how that a good while ago God made choice among us, that the Gentiles by my mouth should hear the word of the gospel, and believe. 15:8 And God, which knoweth the hearts, bare them witness, giving them the Holy Ghost, even as he did unto us; 15:9 And put no difference between us and them, purifying their hearts by faith. 15:10 Now therefore why tempt ye God, to put a yoke upon the neck of the disciples, which neither our fathers nor we were able to bear? 15:11 But we believe that through the grace of the LORD Jesus Christ we shall be saved, even as they.
Again, as you know, DP - Peter's encounter had been towards its later serving not only as a witness that Israel's water ritual under the Law, was merely symbolic within their God given culture: The Law, but as a witness that Paul's work among the once considered unclean Gentiles, was a work of God.
Note what happened as a result of Peter's witness - the multitude concerned about what Paul was doing out among unclean Gentiles then heard Paul out.
Acts 15:12 Then all the multitude kept silence, and gave audience to Barnabas and Paul, declaring what miracles and wonders God had wrought among the Gentiles by them. 15:13 And after they had held their peace, James answered, saying, Men and brethren, hearken unto me: 15:14 Simeon hath declared how God at the first did visit the Gentiles, to take out of them a people for his name. 15:15 And to this agree the words of the prophets; as it is written, 15:16 After this I will return, and will build again the tabernacle of David, which is fallen down; and I will build again the ruins thereof, and I will set it up: 15:17 That the residue of men might seek after the Lord, and all the Gentiles, upon whom my name is called, saith the Lord, who doeth all these things. 15:18 Known unto God are all his works from the beginning of the world.
The overall narrative makes clear that Paul was water baptized; why he was; and so on.