Some people you run into will believe that baptism is necessary for salvation. 

How will you respond?  Keep in mind John 3:16; Ephesians 2:8-9 and do not vary from it.   Perhaps the following will help you:

Faith in Jesus is sufficient for salvation.  You don’t have to do anything; Christ has done it all.  However, baptism is very important and all believers should be baptized by immersion.  If one refuses biblical baptism after salvation it may cast doubt on their salvation experience.

There are denominations that believe baptism is necessary for salvation.  The arguments used, on the surface seem to be powerful, but upon examination, baptism is found to occur after conversion and is not in any way a cause or part of it.  For instance, Christ said to make disciples [believers] and then baptize them by immersion (Matthew 28:18-20).

Acts 10:44-47 follows this example.  While Peter was witnessing, the Holy Spirit fell upon all those who were listening to the message…and they were hearing them speaking in tongues and exalting God.  Then Peter said, “Surely no one can refuse the water for these to be baptized who have received the Holy Spirit just as we did, can he?”

This passage shows that baptism happens after salvation.  How do we know they were saved?  They were speaking in tongues — which is a gift from God (I Cor. 14) to believers.  Non-believers do not exalt God.  Also, Peter said they had received the Holy Spirit (Ephesians 1:13-14) and it happened before baptism.

Another set of verses applicable to the issue is I Corinthians 1:17, where Paul says “For Christ did not send me to baptize, but to preach the gospel…”  The gospel is what saves (Romans 1:16).  See the explanation of the good news [gospel] in I Corinthians 15:1-4.   Baptism is not part of the gospel; it is a step of obedience that a believer takes after salvation and following the example of Christ (Matthew 3:13-17).