I have a leak in the main cold water pvc supply line. The main shutoff valve allows some water to get past and the glued joint fails. How do I repair a leak when water is present?

Turn the water off at the street box if you have city water, power off the well, if so supplied, and then drain the system.

Thanks again, I finally decided to loosen the union connection at the meter and now I have no water issues. I'll glue it up and hopefully, there won't be a leak any longer.

Good luck.

Probably could have used the blue PVC cement.

PVC Rain-R-Shine® Blue Cement | Plastic Pipe Cements & Primers | Oatey (http://www.oatey.com/products/plastic-pipe-cements-and-primers/oatey-specialty-cements/pvc-rain-r-shine-blue-cement)

You could buy or rent one of these https://www.plumbingsupply.com/waterstopperforsoldering.html