If you weren't arrested for a new charge, then this is only a technical violation. In general, Probation understands that sometimes people who use drugs relapse, and while they are not happy about it, they generally do not throw the book at someone in your situation the first time this happens. Probation has a whole arsenal of possible sanctions available to them, ranging from a wrist slap (more intensive supervision, more reporting requirements) on the one extreme to house arrest or revoking probation outright on the other.
They may lodge a violation against you, but what that means and what they will recommend in your case will depend on many factors, such as your background and history, the facts and circumstances of the underlying case, how well you've been getting along with your probation officer, whether you've been in good over all compliance with the terms of your probation before the violation or whether you've given them trouble before.
It will all come down to whether probation thinks that working with you will ultimately turn you into a successful probationer and a productive citizen or whether they think you never will get the message and will want to wash their hands of you.
If you've been doing well, they will likely just increase your reporting and your testing schedule, and you can help yourself now by going to AA-type meetings or by getting counseling and being in a position to point that out to your PO or to the judge. But if they do decide to violate you, you will be entitled to a hearing on the violation. You should have a lawyer at that hearing so that in the unlikely event that probation and the DA are asking for you to be resentenced to jail, someone can make a good argument for drug treatment or house arrest.