Can a diluted urine sample send you back to jail?

It sounds like you were on a court referral program in which you were expected to undergo monthly drug testing and complete a variety of life skills or driving classes. This program would allow you to nolle prosse the conviction so that it does not show up on your record. Additionally, the court may have lessened or deferred fines contingent upon your completion of this program, although in my experience it is common for the court to still assess the fines and only offer the nolle prossed conviction as reward for completion of the program. You should have a non-compliance hearing, where you will get a chance to explain to the correctional officer, prosecutor, and/or judge what happened. A diluted test result usually occurs when large quantities of water have been consumed shortly before a drug test. Unless you drink large quantities of coffee, it is highly unlikely that coffee would result in a diluted drug test. I only bring this up because if you claim to the court that one cup of coffee was what resulted in a diluted test, they are not likely to believe you. If you drank large quantities of water or coffee before the test, the best policy is to be honest about that with the court, because they have enough experience with these tests to know whether what you are claiming is likely to be true. You may or may not be allowed back on the referral program. If you've had no positive tests so far and no history of other alcohol related offenses, then they may allow you to go back on the referral program and give you a chance to still have the charges nolle prossed. If they do not allow you back on the program, however, then they may give you a fine for contempt of court, but it is unlikely that you would have to serve any jail time, unless the judge previously sentenced you to jail time but deferred that sentence contingent on completion of this referral program.