Volume of Water Over a Period

Every water balance on this page produces a rate, and nobody is ever billed for a rate. V = Q·t is the one line that crosses from engineering into accounting: a makeup valve passing 10 gpm is open 1440 minutes a day, so it buys 14,400 gallons of city water a day and about 5.26 million a year. Run it the other way and it is the meter-reading check a technician does on the tailgate — 5256 m³ off the annual makeup meter divided by 525,600 minutes is 10 L/min, and if the calculated balance says 25 L/min then something is running that nobody mentioned.

Two traps live in the t. The first is the operating year: a tower that runs eight months and sits drained through the winter has a 5840 hour year, not an 8760 hour one, and sizing a chemical contract on 8760 overstates it by half. Ask for the run hours and put them in the file. The second is which year you mean — 365 days is 31,536,000 s, while the Julian year used for "per year" units is 365.25 days, or 31,557,600 s. The difference is 0.07%, invisible next to a flow meter's ±2%, but it is the reason two spreadsheets that both look right disagree in the last digit. The deeper mistake is treating any of this as steady: a rate multiplied by a year assumes the rate held all year, and a bleed solenoid that stuck open for a fortnight is a story the annual meter reading tells and the calculation never will.