Convert 20 inches to centimeters, and then calculate the volume of the water in the tank, then we can convert the volume in cm^3 to liters. Here's the formula: Vol = L x W x H = 50.8 cm x 50.8 cm x 25.4 cm = 65548 cm^3
65548 cm^3 x (1 L x 1000 cm^3) = 65.5 liters