Ireland’s small surface area may fool many visitors into thinking they don’t need a car, especially just to visit a single city like Waterford. However, car is by far the best way to see the city, especially since you'll likely already need one to drive to Waterford from another airport. The Irish national bus system is fairly reliable, but it connects Ireland’s major cities, and doesn't offer service to specific points of interest within Waterford. Hiking and biking are nice, but Ireland is hilly, and if you’re unfamiliar with the shortcuts it will take forever to get anywhere. Car (or taxi) is truly the best option.

If you will be driving your own car from within Ireland or on one of the ferries from mainland Europe, all you’ll need is a passport, a valid driver’s license, and an accurate road map. It is also helpful to have some practice driving on the left side of the road. Rental cars are available at all the major airports, though prices are often outrageous considering this is an island with many tourists seeking cars. The best way to avoid getting gouged is to reserve a rental car online before your visit. http://www.rentalcarsireland.com/ is a good place to start, and reservations can also be made through most airports and many hotels.

GoIreland.com has a comprehensive list of taxi services in Waterford.

Waterford & Region - Getting Around Info     This is a comprehensive listing of information from the tourist office.