Yellow water can be caused by rust in the pipes and sediments that make their way into the water supply from the source (the James). The office I work in will suffer from the former when the building has been in disuse for a long period, such as a long holiday weekend, but eventually will come out clear again. If the water isn't clearing out, and it's like that every day the restaurant's owner needs to have that looked into. The water from your soda fountain should not be affected as it should be on a rather beefy filter system, for the chemicals they treat water with along with other minerals that are naturally in the water can affect the flavor of soda, and a lot of soda fountains and bar guns have a filtered flat water option. But as I type this, I just remembered another potential cause of yellow water, and that is caused when carbonated water makes its way back into the water supply lines, for when carbonated water mixes with copper plumbing, it produces carbonic acid, which is not good to drink, so check to see if the carbonator's backflow preventer is intact (this is why everything past the carbonator has to be stainless steel or plastic).