Water in the system, when soldering pipers together?

If you shut the water off to your house at the valve, where it comes in & drain the water at the hosebib right there also, You won't have any problem soldering your lines. You can't solder copper pipe with a lot of water in them. By the way, when you do turn the water back on, turn it back on fairly slowly. You don't want the water to refill the lines in your house TOO fast. Good luck.