Discussions

plumber here. generally not a big deal to shut the water off at the main. Just dont be rammy and crank the heck out of it. If its a 1/4 ball valve, no sweat. if its a meter stop with a round handle, like a tap just be aware that by over cranking, you can break the stem and the water will be off untill you get a plumber, who will have to call the city to shut your service off. good luck

You could get shut off valve installed at the same time for future. You would be paying for the hour anyway and parts wouldn’t be that much.

I have yet to see a water system that doesn’t have a main shut off at the water meter.  
 
As another poster noted, it will either be a ball valve with a lever or a standard tap. If it hasn’t been turned off for a while it may be stuck. Don’t be too rough loosing it. If you break the tap or pipe you’ll get wet and an expensive mess to sop up.

Another option would be to shut off the cold water supply to your water heater. That way you wont have to mess around with your main water supply

Shut off main, or shut off hot water tank inlet valve, drain line, cut off old valve, solder in new one. And DIYer can do this job. Even if you only had the main and it leaker a little, shove some bread inside and solder on the new valve then open it into a bucket to blow out the bread.  
 
(You can’t solder when there is any water in the line, won’t get hot enough to work, so bread acts like a sponge and stops the slow leak so you can solder. Then when you turn the water back on and open the valve the bread comes right out)

Correct. Your hot water is directly. Dependant on the cold water coming into the tank. Isolate the tank. No hot water