Open the shower-head up...remove the piece. It's usually a little screen-thing with rubber around the end.
Now - Neither ME nor DebatePolicy.com advocated going around gov't rules - but you simply want to "TEST" your shower head to insure the device is working or not working...that's how I'd do it.
“… the greatest detractor from high performance is fear: fear that you are not prepared, fear that you are in over your head, fear that you are not worthy, and ultimately, fear of failure. If you can eliminate that fear—not through arrogance or just wishing difficulties away, but through hard work and preparation—you will put yourself in an incredibly powerful position to take on the challenges you face" - Pete Carroll.