If working on a water line and the shut off valve is out of sight, always work in pairs. Phone your partner before you turn the water back on in the case one of your joints did not properly seal. That way you can stop any flooding before too much damage can be caused.
The number 1 tip in plumbing is if you are not 100% confident in the problem AND the solution, hire a licensed professional to do the job for you. Do not risk flooding your house, or causing a long term problem that may not immediately present itself.