What I have done was go to the store and buy 2 gallons of water in 1 gallon jugs. Then on check out have the cashier weigh each jug individually on the certified scale they have (it helps when you know them too, doesnt seem as weird). With a sharpie write the weight on each jug. Then use one or both jugs to test the accuracy of your scale. If I remember correctly the Arrowhead gallons weighed in about 8.75 pounds.