To install a water heater, the sink top must have a hole that can receive the spout. Most hot-water dispensers are installed during kitchen remodeling in new sinks that have the proper number and configuration of holes. Though retrofits can be a little bit tricky, they're not impossible in Arlington, Virginia. If your sink has a sprayer, you may be able to remove the sprayer and use the hole that it occupied. Or, if your sink has a separate spout for purified water, you can replace that one with a hot-and-cold model as explained above. Or check to see if the sink has an extra hole that hasn't been punched out yet. In a real pinch, you can have a plumbing contractor drill a hole in stainless steel or porcelain - though you risk cracking porcelain.

Though units sold through specifiers such as designers, kitchen shops and wholesale plumbing houses are generally installed by plumbers, those sold through home centers, major department stores and hardware stores come with complete instructions for do-it-yourself installation. With most, a "saddle valve" is clamped onto the water pipe, then the appliance is connected to this valve with 1/4-inch copper tubing, using compression fittings. Most appliances have a 3-pronged plug that you simply plug into a grounded, 15-amp receptacle (in some cases, they may share the receptacle used by a garbage disposer, but be sure to follow manufacturer's directions and honor local building codes).