How hard is the water, really?
It depends entirely on your source, and the two answers are far apart. Metro Detroit city water from the Great Lakes Water Authority runs about 99 to 116 mg/L, roughly 6 to 7 grains per gallon, which the USGS calls moderately hard. Private wells in Oakland County run far harder: the median USGS well sample is about 290 mg/L, roughly 17 grains, and 90 per cent are in the very hard band.
Last updated 4 October 2026.
The USGS scale, so the words mean something
| Classification | mg/L as calcium carbonate | Grains per gallon |
|---|---|---|
| Soft | 0 to 60 | 0 to 3.5 |
| Moderately hard | 61 to 120 | 3.6 to 7.0 |
| Hard | 121 to 180 | 7.1 to 10.5 |
| Very hard | more than 180 | more than 10.5 |
Scale published by the U.S. Geological Survey. One grain per gallon is 17.1 mg/L, so the grain columns above are that conversion applied to the USGS bands.
Metro Detroit city water, plant by plant
| GLWA plant | Draws from | Published hardness | Serving (of our area) |
|---|---|---|---|
| Springwells | Detroit River | 101 to 106 mg/L average (about 6 grains) | Canton, Livonia, Northville, Plymouth, Farmington, Royal Oak, and part of Novi and Farmington Hills |
| Northeast | Detroit River | 99 to 105 mg/L average (about 6 grains) | Pleasant Ridge, and blended supply to SOCWA communities |
| Lake Huron | Lower Lake Huron watershed | 99 to 105 mg/L average (about 6 grains) | Novi, Bloomfield Hills, West Bloomfield, Bingham Farms, Troy, and part of Farmington Hills |
These are Great Lakes Water Authority plant analyses, reprinted in member cities' own annual water quality reports: Livonia (101 mg/L average), Royal Oak (101), Berkley, Birmingham and Southfield (105 to 106), Beverly Hills (99 to 101), Plymouth (116) and Lathrup Village (92). Troy publishes maximums rather than averages, at 130 mg/L (Lake Huron) and 120 mg/L (Northeast). The grain conversions are ours.
Several cities in our area publish no hardness figure at all, because hardness is not a regulated contaminant and reporting it is voluntary: Canton, Novi, Northville, Bloomfield Hills, West Bloomfield, Farmington, Farmington Hills, Bingham Farms and Pleasant Ridge. Their water comes from the same plants, so the plant figures above are the honest answer for those homes.
Private wells are a different story
Well water in this region is a different animal. The USGS study of the glacial aquifer system, which underlies Michigan, found a median hardness of 258 mg/L in drinking-water wells, with 74 per cent hard and 64 per cent very hard (USGS Circular 1352, sampling 1993 to 2009).
Closer to home, we pulled the USGS-held well samples for Oakland County from the Water Quality Portal: 460 samples across 346 wells give a median of 290 mg/L, about 17 grains per gallon, with half the samples between roughly 15 and 20 grains and 90 per cent above the USGS "very hard" line. That is our calculation from USGS records, not a figure USGS publishes.
For scale: Michigan EGLE's own guidance calls hardness above 250 mg/L objectionable, citing scaling of fixtures and soap scum. A typical Oakland County well sits above that line, while GLWA city water sits well below it.
We do not publish a hardness number for any individual well, because wells vary street by street with depth and geology. If you are on a well, a test is the only honest answer, and ours is free.
What the number means for sizing a softener
Softeners are sized by how many grains of hardness they remove between regenerations. The rough sum is:
grains to remove each day = hardness in grains per gallon × gallons used per day
A four-person household on GLWA water at about 6 grains, using roughly 75 gallons per person per day, works out near 1,800 grains a day. The same household on an Oakland County well at 17 grains is closer to 5,100 grains a day, which is why well systems are built and priced differently. Sizing is part of what we do on the call, and getting it right is what keeps salt use and running costs sensible.
Find out what yours is
We read the published data for your own supply and tell you what it says, free, with no in-home visit. If you are on a well, we talk through your test results on the call. Request a free water assessment or call (248) 213-7765.
Related reading: softener vs whole-home filtration · salt-based vs salt-free · your city's water supply.
Common questions
How hard is Metro Detroit city water?
Great Lakes Water Authority plant analyses, reprinted in member cities' own water quality reports, run about 99 to 116 mg/L. That is roughly 6 to 7 grains per gallon, which the USGS classifies as moderately hard.
How hard is well water in Oakland County?
USGS-held well samples for Oakland County have a median of about 290 mg/L, roughly 17 grains per gallon, with 90 per cent above the USGS very hard line. Individual wells vary a lot, so a test is the only way to know yours.
Is 6 grains per gallon hard enough to need a softener?
It is enough to scale a water heater, spot glassware and leave soap scum over time. Whether that is worth treating is your call, and we will tell you honestly what we think on the phone.
Why does my city not publish a hardness number?
Hardness is not a regulated contaminant, so reporting it is voluntary. Several cities in our area publish none. Their water comes from the same GLWA plants, so the plant figures are the honest answer.
What is a grain per gallon?
It is the unit softeners are sized in. One grain per gallon equals 17.1 mg/L of hardness, so 100 mg/L city water is a little under 6 grains.
Does hard water harm your health?
Hardness is not a health contaminant and is not regulated as one. It is a nuisance issue: scale, soap scum, spotting and shorter appliance life. Michigan EGLE calls hardness above 250 mg/L objectionable on those grounds.
Is Michigan water harder than the rest of the country?
Michigan groundwater is hard by national standards. The USGS study of the glacial aquifer system underlying the state found 74 per cent of drinking-water wells hard and 64 per cent very hard. Great Lakes surface water, which most of Metro Detroit drinks, is much softer than that.