Know How Long is Alcohol in Your System Discovery Institute Your blood alcohol concentration (BAC) level is affected by several factors, making it difficult to calculate yourself. You could be over the limit and not know it. If you plan to drink, Breathalyzer Tests: Definition, How It Works, Types, How to Read, Accuracy Better Life Recovery Your eyes are your first line of defense. Good BAC Water: Crystal clear, odorless (faint alcohol scent), and painless. Bad BAC Water: Cloudy, particulate matter, strong chemical smell, or severe burning.