Water density at room temperature: 0.99802 g/ml. Convert your 1L figure to mL. Volume = 1 × 1000 = 1000mL. Weight in grams = volume × density. 1000 × 0.99802 = 998.02g. Convert grams to pounds. 998.02 × 0.0022 = 2.1956 lb. To make things easier, and assuming you require a rough estimate, you could use a straight density figure of 1g/ml. More @Wikipedia
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