wrote in message

One unit equals 748 gallons. I believe I pay $3 per unit

True, but your meter probably reads cubic feet. One cubic foot = 7.48
gallons, so, 100 cubic feet as read off the meter is one unit or 748
gallons.

Use care in reading your meter as there are different types. Some are
dials, others have a single dial and numbers like an odometer, some read
decimal points and others do not, some have a multiplier where the meter
reading is X10 (mostly for industrial use). Sometimes even the water
company meter readers don't get it right. I've had the problem of under
billing on one meter, over billing on another, in the amounts of thousands
of dollars.