Just moved into a new house and find that the shower near the garage, where the water heater is, has great water pressure. The shower on the other side of the house, however, has very poor water pressure. I always understood a plumbing system in a house to be a sealed system, so that would mean the pressure should be somewhat equal across the board, correct? What could be causing the low pressure on the other side of the house? Every other house I've ever bought or lived in had good pressure throughout. The house was recently converted to city water and sewer, whereas before it was on well and septic. I don't know if that would make a difference or not. Could something have clogged a line during the conversion? Is the a leak in the system? I'm unsure how to resolve this problem.

I would start by removing the shower head and see if the screen is partially clogged, if not then the cartridge will need to be removed and cleaned or replaced. You are correct that the pressure should be the same throughout the house, for all fixtures on the same level. Naturally pressures will be lower on the 2nd level.

good advice... with the cartridge removed, turn the water back on briefly to flush. also observe the pressure (if you can)..

what kind of water piping do you have?

"Static pressure" meaning NO water is being used IS constant throughout the house. "Dynamic" pressure, however can be affected by the volume of flow, the size of the piping and other factors, and THEY WILL reduce the pressure from one side of the house to the other, especially if the city water was connected at a different location than where the pump was.

If you have good pressure and flow to your house, pressure should be pretty equal. Any major loss in pressure is likely due to a restriction of some type. Restrictions reduce volume which goes along with pressure. Lime and sediment sounds likely unless there was really bad decision making made when the shower was built.