Diagnose Leak and Shut Off Water Supply

all right so I came over to my neighbor's house master bath lab faucet because he has got a drip says it's pretty annoying in the middle of the night would like this change we're going to go ahead I'm going to show you how to figure out which one of these is actually leaking and then we're going to replace the cartridge so come along let's get to fixing so the first thing I like to do is get right here to the aerator and you want to get this off okay this actually comes off pretty easy if it didn't you might have to put some pliers on it or something just be gentle you might Mar it the aerator is always going to hold a little bit of water this is where water and air mix to actually make a nice stream in your faucet we're gonna get underneath here and we're going to start by shutting the cold water line off just make sure we get all the water out of here and then we'll wait I don't see any water there let's turn that back on real oh nope I do get a drip yep okay let's shut the hot side down then I'm just gonna turn the cold back on we've got no drip coming out now so it turns out the hot side is the culprit let's change this cartridge right here