Math CentralQuandaries & Queries


Question from Terry:

I know that a cubic foot of water=7.48051945 gals., but I keep geting my water bill and they go by thousands of a gal. per cubic foot. Is there a conversion that says that shows this? Water department=.763 x cubic foot used=thousands of gallons water used that month. Exampel: 72cu. ft meter reading x .763+ 58.--- galons of water I use in a month. Total 58=thousand = +galons. This is wrong. There are only two people in the house.

Hello Terry.

I note that you are writing to us from the United States. The typical water usage in a small residential home in the United States certainly ranges widely, but is generally between 30 and 100 gallons per person per day. So 5800 gallons is not unreasonable for a monthly billing as far as I can determine, but 58000 is certainly out of whack.

You are right that 1 cubic foot of water is 7.48 U.S. gallons. Many water meters and companies measure in terms of HCF (hundreds of cubic feet). To convert from HCF to thousands of gallons, you would multiply the HCF reading by (7.48/100) = 0.748, which is close to the 0.763 figure you see, but oddly, not the same.

What was your previous bill? If you have a leak in or under your property or at the municipal juncture, then you may be registering a lot more water. An open faucet, or the equivalent through a leak, might output a gallon a minute, which would be about 30 x 24 x 60 = 43000 gallons: not far from the disparity.

If you have used 72 HCF in the billing period, this would be 72 x 0.748 = 54 000 gallons (roughly).

Contact your water utility and perhaps a plumber or engineer.

As well, I cannot explain why they are using 0.763 instead of 0.748. This factor has the effect of a 2% overcharge.

Stephen La Rocque.

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