Final answer:
To determine the number of units of water used during the month, subtract the initial reading from the final reading.
Step-by-step explanation:
To determine the number of units of water used during the month, we can subtract the initial reading from the final reading. \In this case, the initial reading is 312,017 units and the final reading is 320,405 units. Subtracting these values, we get:
320,405 - 312,017 = 8,388 units of water
Therefore, 8,388 units of water were used during the month.