Americans tend to shower every single day, but most don't clean their showers every day, let alone their shower head! I think we all kinda assume that since only water comes out, it can't get that dirty, can it?
Well, overtime it builds up crusties - mildew, hard water stains, hard water spots, calcium, etc. - and they can start to block the flow of water.
Here's the cleaning tutorial you need to easily remove all that junky build-up and get that water cascading down as intended.