Answer:
1 gallon and 1 pint
Step-by-step explanation:
I guess that the actual amount of water needed per player is 1/8 of gallon and not 18 gallons.
You will need to bring 9 x 1/8 = 9/8 = 1 ¹/₈ gallons or 1 gallon and 1 pint
1 gallon = 4 quarts = 8 pints = 16 cups = 128 ounces
or
1 gallon = 3.785 liters
The US is one of the few countries (along with Liberia, and Myanmar) that still uses the imperial system to measure things, e.g. inches, feet, yards, pounds, miles, pints, gallons, etc. The rest of the world uses the metric system, e.g. meters, liters, kilograms, etc.