Undermount sinks are defined by the way the sink is installed in relation the kitchen countertop. Rather than being dropped into a pre-cut hole in the countertop, undermount sinks are installed under the counter. Because of the way they are installed, there is no rim between the countertop and sink. A variety of materials can be used for undermount sinks, including stainless steel, cast iron, solid surface, and copper. Both single-bowl and double-bowl undermount sinks are available.
The biggest advantage of these sinks is that there is no lip or crevice to catch dirt. You can just brush crumbs or wipe spills directly into the sink without anything getting trapped under the sink's rim. In addition to easing clean-up, these sinks also enhance the style of your kitchen. Because the edge of the sink is hidden, they offer a sophisticated, streamlined look to any kitchen's decor. Faucets are often installed in the counter behind the sink or on the wall.
Despite their practicality and style, there are some disadvantages to undermount sinks to keep in mind. Undermount sinks are harder to install than drop-in sinks and are often more expensive. They work best when combined with a waterproof countertop, because the edge of the countertop will be exposed to water. Undermount sinks are a great choice for solid surface and granite countertops, for example, but aren't generally recommended for laminate. Undermount sinks are sometimes installed with laminate countertops even though water damage is a potential concern; if you consider this option, make sure you find an experienced fabricator/installer. Since the bottom of an undermount sink will be an inch or so lower than a drop-in model, it may require more bending over to work in the sink. Also keep in mind that because a custom hole is cut into the countertop for an undermount sink, it may be more difficult to replace the sink later -- so it's especially important to buy a good quality sink.