If your parents are testing you its fine but it could through off the ph and creatine levels if a lab tests it. I have used my own heavily dilluted urine to make a tech happy once that wanted more than the regular 2 ounces. Tap water is not good to use if you live in the city because it has chloride in it which can show up as an adulterant. Do not mix your urine with the QF and leave it in the whizzinator. Urine is full of impurities and will go bad in just a few hours.