Cost of Water Over a Period

This is the line where engineering becomes an invoice. A tower drawing 10 gpm of makeup buys 5,256,000 gallons a year, and at a $3.00 per 1000 gallon commodity rate that is $15,768 — before a cent of sewer charge is added. Run it backwards and it is the audit worth doing every quarter: divide the bill by the metered volume and check that the rate you have been quoting in proposals is the rate the utility is actually charging, because North American water and sewer rates have been climbing faster than general inflation for two decades and a three-year-old spreadsheet is usually low.

Two things to be careful of. The site holds no exchange rates and never will, so the answer comes back in whatever currency you typed the rate in: a rate entered in CAD gives a CAD answer, a rate in EUR gives EUR, and nothing on this site converts one into the other. Enter the rate off the customer's own bill and the answer is in the customer's own money. Second, "the water rate" is almost never one number. A municipal bill carries a commodity charge per 1000 gallons, a fixed meter or service charge that does not scale with volume at all, and — separately — a sewer charge levied on the same metered volume, usually at a higher rate than the water itself. Blend the volumetric charges for this calculation and leave the fixed charge out, since it does not change when you save water. And for a cooling tower this figure is only half the story: what the site actually pays is the makeup bill plus sewer on what is discharged, which is the makeup volume less what evaporated — see the net water and sewer cost, and the evaporation credit that goes with it.