If you have low water pressure problems, here are a couple of things to check. Check all of the strainers on the faucets to make sure they are not blocked. Aerators/strainers need to be removed annually to check for buildup of minerals inside openings and anytime anyone works on the water piping system. Check your main valve coming into the home to make sure it’s not half way open. Check the meter valve to see if it is really open. Sometimes the valve gets stuck in the closed position, even though the handle continues to turn. If it is, then check the piping to see if it is galvanized (use a magnet) copper is not magnetic.
If the piping in the house is made of galvanized metal, then it could be calcium and mineral deposits. When galvanized water pipes are in a home for 30 to 50 years, calcium is leeched out of the water and attaches to the inside of the water pipes. It builds up through a process called ion exchange (magnetic attraction). It takes many years for this to happen and when it does, it coats the full length of the pipe. Unfortunately calcium builds up on the inside of the piping and reduces the internal diameter with pebble like growths until the water can no longer flow. It slows down the water like the rocks in a stream. The deposits are hard, just like the bones in your body, so they cannot be removed. In addition, there is no tool or liquid you are allowed to put into the pipes to clean them out, which you would want to drink later.
If it is galvanized metal, the only solution is to replace the piping. We would recommend replacing all the piping, not just the horizontal sections. Many people make the mistake of having their plumber only replace the horizontals. The problem is, half of the cost is the tear out and it doesn't take any more time to tear out the complete system. The set up time and demolition time is the same for both jobs, but if you do them at the same time, you only pay once.
Once in a while an old galvanized main valve gets stuck halfway open. Gate valves often have problems with the rising stem pulling out of the disk that shuts off the water. Even though it seems like the valve is open, because the inside threads allow the stem to continue turning up to the top of the threads, the valve is closed. Inside each gate valve there is a tapered round disk that fits into a tapered slot. When it's all the way down the valve is shut off. When it lifts up the valve is open. If the valve hasn't been closed in many years, calcium builds up on the ground faces of the slot as the water passes over it. When you close the brass gate, it gets stuck on the rough sandpaper like surface. When you try to turn it up, the stem simply pulls through the brass-casting slot and leaves the gate in place. Once this happens, you have to replace the valve.