People often refer to the blood alcohol concentration (BAC) limit for drivers as if it means that driving with a lower BAC is safe and acceptable. The limit, of course, is .08% for most drivers. If someone has a .06% or a .07% BAC, then they think that they can't get arrested for drunk driving.
That's why people often talk about being able to wait it out after drinking. They have a glass of water and give it a half hour, hoping their BAC dips back below .08% before they have to leave.
While waiting for your BAC to go down is wise, do not assume that getting under .08% means you can't get arrested. You can still get charged with a DWI.
The key to the case lies in what the police see. If they spot evidence of clear impairment, they can still arrest you on the grounds that you are impaired behind the wheel. That's what is really illegal. Not just driving over .08%. Driving while you are impaired.
This rule also helps them arrest you for things besides alcohol. For instance, maybe you took medication that instructed you not to drive. Then you had a beer with dinner. Your BAC is only .04%, but the combination of substances impairs your ability to drive.
As this shows, DWI laws may not be as straightforward as you once assumed. If you get arrested and find yourself heading to court, make sure you have a full understanding of the laws of the case and the legal defense options at your disposal.