If a sink can float, so can a cabinet. Many manufacturers of quality bath fixtures also sell bathroom cabinets -- many of which may be wall-mounted to fit beneath a floating sink. Match your sink to the wide variety of woods, laminates or even metal, tile or glass-fronted cabinets available to create a personalized style perfect for your taste.
If custom cabinets are not in your current budget, you can still get stylish storage space for minimal cash outlay. Invest in a large wicker picnic hamper to store towels and other linens conveniently under the sink, or use large plastic lidded-storage boxes to do the same. Inexpensive wire closet racks and bins offer further options for storage under the sink.
Install a long towel rack or series of shorter, swing-out bars to hang extra towels from, or put a row of hooks under the sink for them. Hang a “back-of-the-door-style” shoe organizer from a hook and use it for those small items every bathroom seems to accumulate -- personal items, shampoos and conditioners, extra soap, hair dryer. You could store folded washcloths and sponges in the compartments as well.
Save money and space in the landfill by upcycling a low bookshelf with a new coat of gloss enamel paint to use for under-sink storage, or dress up an old coffee table to serve the purpose. Many furniture items like nightstands, low dressers, children's desks, stools and storage cubes will fit below a sink and, with fun new paint colors, look stylish there. Don't forget to look for potential storage solutions in unusual places like the kitchen, garden or garage -- buckets and milk or wine crates, an empty cooler, pie safe, sewing cabinet or knickknack shelf may be the very thing you need.
Because water is an ever-present fact of life in and around a sink, make sure that your under-sink solutions don't become problems. Choose items that can handle occasional wetting or plan ahead and paint them with water-resistant enamels or sealers as appropriate.