Most shower heads will start to clog with deposits over time. How quickly depends on how hard the water is where you live. In most case, you can easily remove the hard-water and mineral deposits that build up in a shower head using vinegar in a plastic bag:
1. Pour warm vinegar (50% vinegar 50% water for light duty cleaning) into a small plastic bag sized to fit your shower head. (We usually run vinegar through our coffee maker and then use this heated vinegar to soak our shower head.)
2. Attach the filled bag to the shower head using a rubber band or twist tie. Make sure the entire head is immersed. (Some heads are easier to clean by simply removing the shower head and soaking in a bowl or bucket.)
3. Soak the shower head for at least an hour, overnight is best in most cases. (Chrome is a durable finish. Some finishes may be harmed by extended soaking in some cleaning agents.)
4. Remove and discard the vinegar.
5. Remove the loosened deposits with a toothbrush.
6. Clean the spray holes in the shower head with a toothpick.
7. Run hot water through the shower head for several minutes.
You can use a similar procedure for cleaning mineral deposits from bathroom or kitchen faucets and tub spouts.
Another cleaner that usually works well is lemon juice. Use it full strength or 50/50 dilution with water the same as vinegar. The photos below are before and after of a hard water stained handheld shower. It was soaked about 6 hours in lemon juice and brushed with a toothbrush.
In most cases these natural cleaner will work great. Some areas have minerals (i.e. iron) in the water that are not as easily removed with just vinegar or lemon juice. There are other products sold that will remove these harder deposits. One is CLR. It is available in most hardware (Ace, True Value, etc) and drug stores (Longs, Rite Aid, etc.) Follow the manufacturers instructions.