For those who don't want to replace their PVC valve, this tool is an easy alternative in the 3/4 inch size. It protects the valve handle from breaking, and makes it very easy to turn it off and on.
https://www.amazon.com/gp/product/B0...e?ie=UTF8&th=1
Note that you may also have a PVC valve on the cold water pipe near the water heater. This valve can come in handy if your water heater or expansion tank starts to leak. It will allow you to shut off the hot water, but still have cold water in the house. If you shut off the main valve, you will have no water.