When you’re a designated driver, do you stick to water or soda? Luckily, most people do. But not all of them.

A new survey reveals that 35 percent of designated drivers haven’t completely abstained. That’s one-third of all designated drivers. Worse, most had blood alcohol levels that would impair their driving—the very thing they are supposed to be doing safely. In fact, half of the designated drivers who drank alcohol recorded blood alcohol levels higher than .05 percent.

While .08 percent is the current legal limit for drunk driving, .05 is being suggested as an update to that threshold. The National Transportation Safety Board recently recommended a .05 limit for all 50 states. The U.S. has one of the highest allowable legal limits among developed countries.

Researchers said designated drivers are often chosen by who is the least drunk, or who in the past has successfully driven while intoxicated. It’s also possible a driver is not designated in advance. Or, it could be, the designated driver believes one or two drinks won’t affect his or her driving abilities.

Obviously the best and safest choice for any designated driver is to remain completely sober.