The board shall cause to be kept separate and complete records of all income and revenues from the building, facility or improvements and the use thereof and services rendered therewith; and all of the operating and maintenance expenses thereof, and none of said income and revenues shall be expended except to pay the reasonable operating and maintenance expenses as hereinbefore provided, and to pay principal and interest on bonds issued under the authority of this act [6-17-1 to 6-17-13 N.M. Stat. Ann., except 6-17-1.1 N.M. Stat. Ann.].