The most common cause of dilute urine is over-consumption of liquids. You will need to tell me what kind of treatment coordinator you are referring to.
When they do drug tests in a program such as this, they also test for specific gravity to make sure the urine has not been diluted to obscure the use of drugs. Normal urine specific gravity is 1.002 to 1.028.
There are very, very few medical reasons for dilute urine. Medically, it is far more common to have concentrated urine. The few medical reasons are diabetes insipidus (a condition in which a gland problem causes someone to drink gallons of water per day, and urinate an equal amount) or renal failure (when the kidneys are unable to concentrate urine), conditions that don't cause dilute urine until someone is quite ill.
I'm sorry, but there is no other medical explanation. You can read more about it below, but you need to understand that urine specific gravity simply doesn't fluctuate all that much unless there is a serious underlying condition such as diabetes insipidus, kidney failure, or severe kidney infection. I suggest you think about other reasons you could have had dilute urine - a night out with too much beer and chips/salsa followed by a killer thirst the next morning that led to drinking lots of water. If you haven't a history of kidney problems, you aren't likely to convince anyone of a medical reason for the dilute urine.