Acts 22:16
16 And now why tarriest thou? arise, and be baptized, and wash away thy sins, calling on the name of the Lord.
This verse, which is part of Paul recounting his conversion experience to a multitude in Jerusalem, is one of the main prooftexts used to teach Baptismal Regeneration.
Such see the mention of "wash away thy sins" to be referring to receiving eternal Salvation. Is this a reasonable interpretation?
We are given the account of the Apostle Paul's conversion three times in the book of Acts:
The account begins by Paul seeing Christ in a bright light (Acts 9:3-5, 22:6-9, 26:13-15), and receiving a commission to preach Salvation by faith, and not water baptism:
Acts 26:17-18
17 Delivering thee from the people, and from the Gentiles, unto whom now I send thee,
18 To open their eyes, and to turn them from darkness to light, and from the power of Satan unto God, that they may receive forgiveness of sins, and inheritance among them which are sanctified by faith that is in me.
He then gets told by Christ to go into Damascus (Acts 9:6).
From the account in Acts 9, we learn that Paul's encounter with Ananias - the person speaking in our verse in question - happened in Damascus three days after his encounter with Jesus on the road to the city:
Acts 9:8-9
8 And Saul arose from the earth; and when his eyes were opened, he saw no man: but they led him by the hand, and brought him into Damascus.
9 And he was three days without sight, and neither did eat nor drink.
The idea that Paul still didn't believe that Jesus was the Christ - thereby receiving Eternal Life (John 6:47), the indwelling of the Holy Spirit (Ephesians 1:12-13), and the new birth (1 John 5:1) - until three days later, is completely uncompelling, considering he immediately obeyed what Christ told him (Acts 9:8, 22:11, 26:19-20), and called Jesus "Lord" when speaking to Him after Jesus had identified Himself (Acts 9:6, 22:10).
After three days of being blind, Paul makes it to Damascus. Here, he meets with Ananias, and receives the outpouring of the Holy Ghost, and his vision, decidedly before being water baptized:
Acts 9:17-18
17 And Ananias went his way, and entered into the house; and putting his hands on him said, Brother Saul, the Lord, even Jesus, that appeared unto thee in the way as thou camest, hath sent me, that thou mightest receive thy sight, and be filled with the Holy Ghost.
18 And immediately there fell from his eyes as it had been scales: and he received sight forthwith, and arose, and was baptized.
Acts 22:13-16
13 Came unto me, and stood, and said unto me, Brother Saul, receive thy sight. And the same hour I looked up upon him.
14 And he said, The God of our fathers hath chosen thee, that thou shouldest know his will, and see that Just One, and shouldest hear the voice of his mouth.
15 For thou shalt be his witness unto all men of what thou hast seen and heard.
16 And now why tarriest thou? arise, and be baptized, and wash away thy sins, calling on the name of the Lord.
Notice that until Ananias "put his hands" on Paul (Acts 9:17), he was blind. Then, Ananias says that he will "receive thy sight, and be filled with the Holy Ghost" (Acts 9:17). These two things happen simultaneously, and Paul can now see. Then, afterwards, he gets water baptized.
This parallels other accounts in the book of Acts, where people received the outpouring of the Holy Spirit, which had accompanying it signs and wonders, by the "laying on of hands" (Acts 8:14-18, 19:6).
Why then, if Paul already had Salvation, and both the indwelling and outpouring of the Holy Ghost, does Ananias tell him to "wash away his sins" by being baptized?
Very simply, this is because water baptism is the first step in obedience after Salvation (Acts 8:36-38), "the answer of a good conscience toward God" (1 Peter 3:21), and a public witness to the fact that you are a Christian. In Paul's case especially, this was a requirement for his fellowship forgiveness with God - "washing away his sins" in that sense - because up to this point he had garnered fame (Acts 9:13-14) for the zeal with which he persecuted Christians (Acts 8:1-3, 22:4-5, 22:19-20, 26:9-11, Galatians 1:13, Philippians 3:6).
Even though, as believers, Christ has "washed us from our sins in his own blood" (Revelation 1:5) in the eternal sense, we still have a temporal relationship with God that requires daily confession and repentance. Likewise, this temporal relationship requires a temporal "cleansing" ("wash away thy sins") and restoration of fellowship with God, as is spoken of here:
1 John 1:6-9
6 If we say that we have fellowship with him, and walk in darkness, we lie, and do not the truth:
7 But if we walk in the light, as he is in the light, we have fellowship one with another, and the blood of Jesus Christ his Son cleanseth us from all sin.
8 If we say that we have no sin, we deceive ourselves, and the truth is not in us.
9 If we confess our sins, he is faithful and just to forgive us our sins, and to cleanse us from all unrighteousness.
So, the blood of Christ is both our means to obtain eternal redemption (Revelation 1:5), and the means to restore our "fellowship" (1 John 1:6) with God throughout our earthly lives - something covered more in this article, which deals with some fellowship forgiveness passages from the Gospels (Matthew 6:14-15, 18:33-35, Mark 11:25-26).
You don't get to Heaven, though, by confessing sins, or by being water baptized. The Bible makes it clear, in scores of verses, that our faith in Christ is solely what justifies us in the eternal sense before God (Acts 13:39, Romans 3:21-22, 3:28, 9:31-32, 10:4, Galatians 2:16, 3:11, 3:21-24, Philippians 3:9, etc.).
In summary, this verse does not teach Baptismal Regeneration. This doctrine is covered at length in its own article, which contains a few proofs that water baptism cannot possibly be a requirement for Salvation.
Rather, it teaches the reality that sins can still affect our fellowship with God, while we live out our lives here on earth. Such things, though, have nothing to do with whether or not we are going to Heaven when we die.