When adding or rehabbing the bar in your home, a big decision is whether change the sink or, if you don’t already have a bar sink you have to decide if you should add one. If you have the space for a bar sink and have plumbing connections in place then it really is not much of a decision. Adding a sink in your bar is relatively inexpensive when all you have to worry about is the actual sink. If you have to have the plumbing connections brought in, it is an entirely different story.
If you do have water lines and a drain in place at your bar, adding the sink is just a matter of having it mounted in or under the counter. I will get into the different styles of bar sinks in another post, but plan on blocking off some time in order to choose the right bar sink for your situation. So you have gone through all the choices in bar sinks, picked one out, and have the water and drain nearby. Now you need to have the sink mounted. Depending on the material the counter is made of, mounting your bar sink may or may not be something you can do yourself.
If you already had a sink and you are changing sink types or sizes, you may be able to modify the sink hole, hook up the drain and water lines yourself, and save some money that would have gone to the plumber. Remember this rule of thumb; when in doubt, let a professional do it. If 
you have a nice home and a nice home bar, the last thing you need is your new bar sink having your counter top butchered by your attempt to mount the sink. If it is a drop in type bar sink the flange of the sink will cover the edges of the counter so you may be able to pull it off. But if it is an undermount bar sink or a vessel bar sink then the counter edges around the sink will be exposed and must be finished properly in order for the sink to look right.
In the case of a bar where there is no current plumbing, you must consider the expense involved in getting the water and drain to your bar. People are constantly surprised at how expensive this can be. The drain is usually a bigger problem than the water lines. Water lines can often be run from the nearest kitchen or bathroom. The drain, however, is more complicated. Drains are gravity devices, and the drains in your home were put in place before the first piece of lumber was used. In order to add a proper drain to a new location, your plumber will have to tap into an existing drain. This may not be as easy as it sounds. Depending on the layout of your house and the location of your bar within that layout, putting in your new bar drain can cost into the thousands of dollars if you are unlucky.