There are a few ways to tell if urine is synthetic. The first way is to look at the color. If the urine is clear or light yellow, it is likely synthetic. Another way to tell if urine is synthetic is by looking at the bubbles. If there are no bubbles, or very small bubbles, in the urine, it is likely synthetic. Finally, you can try smelling the urine. Synthetic urine will often have no odor, or a very faint odor.