I'm taking drug tests for probation and i'm clean but they keep coming back diluted?

I don't do drugs, first off. I don't even drink. I used and that is why I am on probation. I've been clean for almost six months now, but when i go in for my probation i get diluted tests, which my probation officer counts as positive. She says if i get one more diluted i'll have to go back before the judge, which means i'll have violated my probation and won't be able to get my record expunged under the law. I'm scared because i'm a good kid who just made a mistake and now this could ruin my life. I always drink a lot of water beforehand because they watch me while i pee, and i can't do it while someone watches. My question is what should i do, and would caffeine make my test come back diluted?