Since there are 16 tables with 250-milliliter bottles on each, the total amount of syrup required for all the tables is:
250 mL/bottle x 16 bottles = 4,000 mL
Since the bottles are half full, the amount of syrup required to fill all the bottles would be:
4,000 mL ÷ 2 = 2,000 mL
Converting 2,000 mL to liters:
2,000 mL ÷ 1,000 mL/L = 2 liters
Therefore, the owner would need 2 liters of syrup to fill all the bottles.