If you've ever cleaned soap and grime from around the rim of a traditional drop-in bathroom sink, you'll appreciate the easy maintenance of an undermount sink. With an undermount model, the bowl rim rests between a substrate and the countertop material or is supported by glue, brackets, clips, plywood, or another type of framework secured beneath the countertop. This eliminates a ridge around the sink and allows you to sweep stray water spray and soap scum directly into the sink.
Another advantage of an undermount sink is it offers a clean look, allowing your countertop material to take center stage.
One disadvantage of an undermount sink is that it is more difficult to remove and replace if it is damaged. So select a high-quality sink that's under warranty and is designed to last for many years of service.