Final answer:
To record a city's water usage in gallons, DECIMAL(10, 2) would be an appropriate data type, allowing large quantities with decimal precision.
Step-by-step explanation:
For measuring the water usage of a city in gallons, a suitable data type to store this information in a database would be DECIMAL or NUMERIC. Since cities might use water in large quantities and precision is also necessary, it is important to choose a data type that can handle large values with decimal accuracy. For example, you might use DECIMAL(10, 2), where 10 is the maximum number of digits the number can have, including both sides of the decimal point, and 2 represents the number of digits after the decimal point. This would allow for a maximum value up to 99,999,999.99 gallons, which should be sufficient for recording a city's water usage.