5 things all home owners should know about their plumbing system.

1 - Locate and make sure your emergency water shut off valve is working properly.
Generally there are 2 ways to shut off the incoming water to your home, the first at the building and second at the water meter / Well. The one at the building is generally easier to operate and should be checked once a year to verify it is functional. You don't want to be looking for your Emergency shut off valve while your house is flooding.
                                    
                        Water service emergency shut off valve.
                        Example only, can be other types and locations.
                        

                                      Typical  water meter valve.

                                  
2 - The sewer clean out should be where your building drain connects to the sewer as it exits the structure, within about 18".
In an emergency you don't want your plumber looking for your clean out for an hour at 2am, this gets expensive.

                                      

                                                         Typical sewer clean out.

3 - If your home is backing up ( toilets, shower over flowing ) immediately shut off all running water, your drains are connected and water running out of a clothes washer or any other fixture / appliance can end up on the floor in another room.

4 - How to turn off the electric / gas to your hot water heater, Which you will have to do if your tank is leaking and you turn off the water supply to your water heater. Very Important!

5 - How to shut off the incoming water to your hot water heater, if you have a tank leak you must turn off the power/gas and only then turn off the water. This way at least you will have cold water until your Plumber is able to get to you.