John - I do not have all the specifics regarding use of the ex URY water cars on the DRGW or Silverton Branch, but do know that two were assigned to work train service in the later years. I would imagine that they were used for that purpose as well as needed for other purposes all over the remaining narrow gauge. Bradshaw and the D&S received those final two URY water cars as part of the sale of the branch in 1981.
Below are photos I snapped in 1986 with one being used to transport water for the contractors rebuilding of the high-line wall.