Theres a few advantages synthetic has over real human urine. For starters, synthetics far outlast real pee when stored at room temperature. Sure you can obtain a human sample for a sub, but you have to ask yourself:

- Is the sub donor truly clean of any drugs, including scripted and OTC meds?

- Has the sub donor consumed large amounts of fluids (intentionally or not) prior to giving you the sample?

To avoid these kinds of worries, synthetic urine is the way to go.