20 liters of water would be around 5.28 gallons of water.
One gallon of water is around 3.78 liters so if you have 20 liters of water there would be 5.28 gallons of water or almost 6 gallons of water.
If you have 6.08 gallons of water you would have 23 liters of water.
One half gallon of water is equal to around 2 quarts of water or 1.9 liters of water.