When law enforcement officers make an arrest, they typically make an arrest for DUI or driving under the influence and investigate as they would for those offenses rather than OWI. Even after an arrest, they may ask someone to take chemical testing or undergo chemical tests such as urine, breath, or blood tests.
The OWI charge typically comes later when prosecutors are making decisions on how they are going to charge someone. Sometimes they may charge someone with both DUI and OWI, however, it is important to remember that at a trial, a person cannot be convicted of both charges.