Last Year I bought a new house. One of the two showers has low water pressure. Since the House was under warranty, I reported it to the builder who had the sub come out. They said the pressure in the bathroom was ok. it was due to water saving devices. I took out the water saving devices, bought better shower heads, but nothing worked. I even used the same shower heads in both bathrooms and I could notice a difference.
Before I called the builder, I noticed my water department offered a free water flow test. They cam out and said I had 38GPM at the meater, but on 13GPM at the outside just before it came in the house. They indicated 15GPM mininium would be acceptable. They said they was definetely a problem in the pipe running to the house.
I called the builder back, who came out and tested the pressure at the side of the house and said it was fine. He said they do not test water flow. He indicated that because there was 3/4 pipe running to the house is what caused the reduction of the flow. I called the water company who said that was not true.