Douglas, I have this to offer if it helps any;
Some Causes of Low Volume Water Supply
Most low-pressure problems are some times created in the home. The home has adequate water service pressure, but pressure at fixtures drops when another fixture is turned on. This is most commonly encountered when someone flushes a toilet when another person is in the shower. Usually the problem is the water volume is lowered or restricted, reducing the amount of water that comes out of the fixture. Here are some common causes of low water volume. You may have a combination of these problems.
1. Internal plumbing pipes are too small
Water is distributed to your home in a 3/4" or 1" line which can provide a lot of volume and pressure. But, in many homes, internal piping is only 1/2" or less. This reduces the volume of water up to 75%, and can cut the pressure up to 75% as well.
2. Small pipes and a long way to go
In addition to smaller pipes, the problem is worse when water has to go up more floors or travel long distances. This often happens when an additional bathroom and fixtures are added to an older home, but the smaller pipe size is not upgraded. If you’re planning to remodel, be sure to have the water pipe diameter increased to an adequate size.
Long runs of smaller piping reduce the volume of water that can pass through piping, regardless of supply pressure. This is the most common cause of reduced pressure we see in homes in our area.
3. Devices that can affect the volume
Devices such as water softeners, water filters, flow restricting fixtures and decorative faucets can further restrict the volume of water flow in a home.
**4. Piping is getting clogged **
Rust and minerals can build up in older, galvanized plumbing and restrict the flow of water.
5. High on a hill
If your home is at a higher elevation, your water pressure may be below average. If it is below 40 pounds per square inch, a plumber can offer tips for increasing the volume of water to your fixtures.
Talk to a reputable plumber. Usually your plumber can recommend solutions that can enhance your water volume.
Water pressure: the force of water pushing on a unit area, usually measured in pounds per square inch (psi).
Static water pressure: water pressure, measured in psi, at the service line when there isn’t any water running.
Residual water pressure: water pressure at the service line when water is flowing.
Water volume: the amount of water that a pipe can supply. A 1/2" pipe can only deliver a certain amount of water per minute regardless of water pressure.