When you take a unrine drug test, one of the things they look for is the color of the urine. If it's too clear, that means you have been drinking liquids in large quantitys. They will get suspicious.

How far into the horizon is this drug test and how much did you smoke? If you are a skinny person and it was only a gram, you should be clean in another day or so. At least that' what I remember back from those days.... O_o