Mains-connected water coolers have many benefits over traditional bottled water coolers. Most importantly, main-connected water coolers have an endless supply of water. They use an internal element to filter and clean water from the water mains and can also heat or cool the water on demand. Traditional water coolers rely on someone replacing the water bottles regularly which in the end can be more expensive than a main-connected water cooler. So from both a convenience point of view and a money-saving argument, the benefits of plumbed-in water coolers seem to outweigh any advantages of traditional bottle-fed water cooler units.