A homeowner pulls up the city's water quality report and reads a hardness number. The plumber runs a strip at the kitchen tap and gets a different one. Neither of them is wrong. The report describes a system over a year. The strip describes one house, today. Knowing why they differ is the difference between a plumber who reads water and one who recites it.
The report tells you what the city sends out. The tap tells you what this house gets. Read both, in that order.
Short answer
The hardness on a city report is a range of samples taken at the treatment plant over twelve months, printed in milligrams per liter. The hardness on a test strip is one reading at one tap on one day, in grains per gallon. They can only match by accident. The report gets you in the neighborhood. The strip gets you to the house.
Sampled where the water leaves the plant, not where it arrives. Printed as a range, and often an average, across the whole year. One line for a system that may serve a hundred thousand people. In milligrams per liter, so divide by 17.1 to get grains.
Read at this kitchen sink, this afternoon, after whatever blend the system is sending this season, through whatever equipment is already in this house. In grains per gallon. It is the number the equipment gets sized to.
Two real reports
Here is what two utilities actually print. Neither one gives a single number, because neither one has a single number to give.
| Report | What it prints | In grains | Why it is a range |
|---|---|---|---|
| Sachse, Texas | 2025 report, page 3. Total Hardness as CaCO3: 96.0 to 200 mg/L, with 200 listed as the level detected | 5.6 to 11.7 | Twelve months of samples. The low end is moderately hard. The high end is very hard. Same system. |
| Carlsbad, imported | District report, page 2, Skinner plant. Hardness: 165 to 291 ppm, average 228 | 9.6 to 17.0, average 13.3 | Imported water, treated at Lake Skinner. |
| Carlsbad, desalinated | Same report, same page, desalination plant. Hardness: 43.7 to 79.6 ppm, average 56.12 | 2.6 to 4.7, average 3.3 | Desalinated seawater. Soft to moderately hard. Blended into the same system as the row above. |
Milligrams per liter and parts per million (ppm) are the same number for water. Grains are the milligrams divided by 17.1. The scale is the U.S. Geological Survey's: soft 0 to 60, moderately hard 61 to 120, hard 121 to 180, very hard above 180 mg/L. The conversion is explained in grains per gallon explained.
Look at the Carlsbad rows. A house getting mostly Skinner water can read 13 grains. A house getting mostly desalinated water can read 3. They are in the same city, under the same report, and the report cannot tell you which house is which. Carlsbad is also served by three different water districts, so two houses a few streets apart may not even be reading the same report. The full picture is on Carlsbad water quality, district by district.
Why they differ
A system that draws from more than one source or plant sends out a different mix at different times of year. The report averages all of it. The tap gets whichever mix is flowing today.
Sachse prints 96.0 to 200. A strip run in that city will land somewhere inside that range on any given day. It will not land on both ends at once, and it will not land on the average.
A softener in the garage the homeowner forgot to mention reads soft at the kitchen tap no matter what the city sends. The report has no idea it is there. The strip finds it in sixty seconds.
Hardness does not change much in the pipe, but the sample point is still the plant, not the house. The strip is the only reading taken where the homeowner actually lives.
Hardness is not regulated by the U.S. Environmental Protection Agency (EPA). It is on no federal list, primary or secondary, so no utility is required to publish it. In four of the seventeen cities on this tour the utility publishes no hardness figure. Then the strip is the only number there is.
The order
The difference between the two numbers is not a problem to solve. It is the sequence of the job.
Find the disinfectant line and the hardness line. Convert the hardness to grains. Now you know what range to expect and you know whether the city uses chlorine or chloramine before you pick a strip. If the report prints no hardness, you know that too.
Hardness in grains, total chlorine, and total dissolved solids (TDS). Sixty seconds. Now you have this house's number.
The city reports 5.6 to 11.7 grains. Your tap reads 9. That one sentence tells the homeowner you read their report, you tested their water, and the two agree. It is the most credible sentence a plumber can say in a kitchen.
When the strip lands outside the report's range, that is information, not a mistake. A house reading soft in a hard city has a softener somewhere. A house reading far harder than the report in a city with one source is a reason to run the strip again, and then to ask about a well.
Watch it
Questions
The report is a range of samples taken at the treatment plant over a year, in milligrams per liter. Your test is one reading at one tap on one day, in grains per gallon. Divide the report's number by 17.1 to compare them. A tap reading that lands inside the report's range is normal. One that lands outside it usually means a softener is already on the house or the water comes from a well.
Both. The report is right about the system. The strip is right about the house. Equipment gets sized to the house, so the strip is the number that goes on the quote, and the report is the number that tells you whether the strip makes sense.
Because the utility samples through the year and hardness moves with the season, the source and the blend. Sachse, Texas prints 96.0 to 200 milligrams per liter for 2025. Carlsbad, California prints two separate rows, 165 to 291 for imported water and 43.7 to 79.6 for desalinated water, because it sends out a blend of both.
No. Hardness is not on the U.S. Environmental Protection Agency's primary or secondary standards, so no utility is required to print it on the annual report. In four of the seventeen cities on the HALO Water Tour the utility publishes no hardness figure. In those cities the test at the tap is the only number there is.
Yes, every time. The report gets you to the right neighborhood and the strip gets you to the house. Saying both numbers to the homeowner, the city's range and this tap's reading, is what shows you read the report and tested the water instead of guessing.
Sources
Checked in October 2026. Reports are reissued every year, so confirm with the source before you rely on a number.
Written by Roger Wakefield, Texas Master Plumber
45 years in the trade and LEED AP. Published . More about Roger or visit rogerwakefield.com.
Keep going
Day one of the HALO Water Tour is reading a water quality report the way an inspector reads it and running the field test correctly. Carlsbad October 27-29 and Dallas November 3-5, 2026. Twenty seats a city.