What does water baptism achieve in this age?

The only thing water baptism achieves for a person in this age is that it gets them wet. 

There is a baptism involved in salvation during the dispensation of grace, but it is a spiritual one rather than a water one:

1 Corinthians 12:13 (KJV) For by one Spirit are we all baptized into one body, whether we be Jews or Gentiles, whether we be bond or free; and have been all made to drink into one Spirit.

And there are no other baptisms relevant to the body of Christ:

Ephesians 4:5 (KJV) One Lord, one faith, one baptism,

The apostle to the Gentiles is clear in his ministry:

1 Corinthians 1:17a (KJV) For Christ sent me not to baptize, but to preach the gospel: