The valve seat or washer on the main valve are not seating/sealing properly.
It's a valve that regulates the main water pipe.
Water not on at street 'city' valve, or other valves--after inside main valve--off.
There is usually a main water valve that comes into the house, locate this valve and turn it down. Installing a pressure reducing valve after water main valve will allow for adjustment of water pressure to proper setting.
A water Toby is a shut valve at a water main
You turn off the water valve before it -probably on the sidewalk, or just on your front yard. Then remove the main valve and replace it. NOT a job for amateurs. I hope you have some experience at least.
Either toilets seeping through flapper or ground water would be my guess
Outside at the main shut off valve. Showers/Bathtubs do not normally have a shutoff valve like sinks and toilets. The main water valve for the house must be turned off.
Water will run until a valve or pump is shut off upstream from water main break.
After a main water valve is closed the system's PVC pipes are still full of water and will drain to the lowest sprinkler head until the system is empty.
The check valve is a directional valve. Hot water needs to be piped from the top of the tank to the fixture, because that is where the hottest water in the tank is. If a return line is tied into the bottom of the tank, a directional valve (check valve) should be installed between the heater and the pump. That's what they taught me don't know if it really matter upstream or down stream. If you don't have a check valve the water could flow through the return line to the fixture instead of through the supply pipe and the water at the fixture might not be hot enough.
The main Pressure Reducing Valve (PRV) can typically be anywhere between the City Water shutoff valve by your water meter (if external) and the first "tee" in the water supply system. Though quite often it is near the main building shutoff valve inside the home.Some fixtures or appliances have their own PRV, like a hydronic heating system.
The address of the Running Water Historical Society is: 5609 Main St, Running Wate, SD 57062