In a 30 day period, how many gallons of unaccounted for water are there if a supply purchases 4,500,000 gallons and sells 3,900,000 gallons?

To determine the amount of unaccounted for water in the scenario presented, one must look at the difference between the water purchased and the water sold.

The supply purchased a total of 4,500,000 gallons and sold 3,900,000 gallons. To find how much water is unaccounted for, subtract the amount sold from the amount purchased:

4,500,000 gallons (purchased) - 3,900,000 gallons (sold) = 600,000 gallons (unaccounted for).

Thus, the correct answer is based on this simple calculation, where the figure representing the unaccounted water (600,000 gallons) indicates potential losses due to leaks, meter errors, or other inefficiencies in the water distribution system. This metric is important for water utilities to understand their system's performance and identify areas needing improvement or investment.