Meter readers of the Bureau of Water Works shall be paid additional compensation over and above their salary as an allowance for bus fare while traveling in the line of duty is such bus fare has not been paid directly by the Bureau of Water Works.  The additional compensation to be paid each meter reader shall be at the rate of $17.50 per month, which shall be prorated for any part of a month in which the employee has not been required to pay his own bus fare.