Can you imagine an indoor kitchen without a sink? Of course not. That is why most outdoor kitchens designed today include one.
It seems, however, a lot more decisions come with the outdoor sink than the indoor one. Does it need hot water? Where will it drain? How will it be winterized?
Plumbing for an outdoor kitchen sink is similar to other utilities for the outdoor kitchen, it is less expensive to do if the outdoor kitchen is located next to the house. If the outdoor kitchen is against a wall of the home, the plumbing can frequently be run through the exterior basement (above ground) wall and into the kitchen. If not, then the plumbing will require more work. Following are some of the options and considerations...
Hot and Cold
Many outdoor kitchens do not need hot water, and it can be less expensive to run just cold water plumbing. If hot water is desired, compare the cost of an in line (or on-demand) water heater to the cost of running the hot water lines.
If the outdoor kitchen is in a frost zone, any plumbing will need to be winterized before it freezes. The plumber working on the project will design the system and should train the homeowners on the winter shut down and spring opening procedures. Typically, a shut off valve is located inside the home so that the water to the kitchen can be turned off. On the kitchen-side of the valve, but still inside the house, a drain is placed so that water in the lines can be removed. In some situations, pressurized air is used to ensure all water is removed from the pipes and plumbing fixtures. This procedure is similar to that which is used on automated sprinkler systems.
What do you do with the waste water? That is a bigger question, and there are a lot of options.
If you tie the sink into the home's waste water system, you should be free to use a garbage disposal in the sink, and use the sink much as you would an indoor kitchen sink.
Probably the most common solution to a remotely-located outdoor kitchen is to drain the sink into a French drain or a dry well. This will also limit the use of the sink somewhat. You won't want to put food down the sink because of the risk the French drain or dry well will begin to smell.
If these first two approaches are not options, the simplest solution, and the one chosen more often that we might guess, is to drain straight into a bucket under the sink. Emptying the bucket (or forgetting to) can be messy, and it limits the use of the sink, but it can work.
The most green solution is to recycle the waste water (which is considered "gray" water) for use in the garden. This can be done via the "bucket method," or the sink can drain into an irrigation reservoir.
Choosing the Sink and Faucet
One of the most common questions we get at Kalamazoo Outdoor Gourmet is which faucet or sink to choose.
For the sink, stainless steel is the default choice. It is the most durable and hygienic solution. Just about any high-quality stainless steel sink will do the job outdoors, but make sure it is at least 304-grade stainless steel. Other popular options include solid copper or solid bronze sinks. These will patina over time, so be sure the homeowner is comfortable with the earthy or rustic look. Avoid copper or bronze sink "finishes."
For the faucet, you can choose a solid stainless steel unit, but those are pretty uncommon. The most frequent solution is a solid brass faucet with a PVD (physical vapor deposition) finish. A wide variety of finishes are appropriate as long as they are created with the PVD process. Avoid faucets with lightweight or integral plastic parts, and beware rubberized buttons that can degrade with UV exposure. Ceramic disk valves are generally considered best for outdoors.
So, there is no reason to be afraid of including a sink in the outdoor kitchen. Just be sure the homeowner knows what to do to winterize it, and make sure the plumber makes it as easy as possible to do.