The distribution of water from the showerhead is erratic because there is a calcium buildup in the grooves of the showerhead. There are two things that can be done to return proper flow of water through the showerhead. Unscrew and dismantle the showerhead. Remove the calcium with a small penknife or a toothpick. The other way is to place a small plastic bag filled with a few ounces of vinegar over the showerhead. Hold the bag in place with a rubber band and let the vinegar soak into the showerhead overnight. It is best to have the showerhead submerged in the vinegar. Flush the showerhead thoroughly the next morning.