In addition to the obligatory refrigerator full of soda (or sometimes empty of soda, depending on whether anyone’s filled it recently), we also have a water cooler that takes the big 5gal water bottles. They also sell coolers that can be plumbed into a water line, and a while back I discovered that they’re actually bottle-type coolers that come with a conversion kit. The kit consists of a float switch and a solenoid valve, and a mounting bracket that takes the place of the bottle holder.
There isn’t a conversion kit for the cooler we have, but it looked simple enough, so I made one from scratch. I don’t like float switches, so I used two other methods of sensing the water level (I wanted a backup sensor because certain failure modes could result in an unlimited amount of water on the floor, which would be a Bad Thing). Instead of trying to find the “best” way to do it, I used the components I was interested in learning about.
For more details, see the wiki page: