What is this? Thanks for asking!
This is a cold water supply at the top of a water heater. Over time a slow leak can turn into a big problem. As you can see, the water has rusted the top of the tank. This tank needed replacement.
Take a quick look at your water heater, are the fittings corroded or discolored?
Some can be repaired, others are too far gone and need a complete tank replacement. Not sure if everything is ok?
Sent us a couple of pictures, and we will be happy to take a look for you.
Text photos to 781-893-4700 or email them to bmurphy@steelhillplumbing.com