Ann Arbor Water Hardness: What the City's Own Data Says About Softener Sizing

Ann Arbor tap water averages 7.4 grains per gallon (126 mg/L as CaCO3) of hardness, according to the City of Ann Arbor 2025 Consumer Confidence Report. The seasonal range runs 4.3 to 10.5 GPG. At 7 GPG, the Water Quality Association classifies water as hard. Ann Arbor sits at that threshold on average and above it for most of the year. That is the headline finding, and it determines how you size a softener for a Washtenaw County home.

Ann Arbor water quality by the numbers

The table below draws from the City of Ann Arbor's most recent Consumer Confidence Report. These are finished-water values measured at the Barton Pond Water Treatment Plant after treatment, not raw Huron River readings. The ranges reflect seasonal variation over the 2024 test year.

Method note: Parameters compiled from the City of Ann Arbor's publicly available Consumer Confidence Report and city PFAS program pages. All figures reflect post-treatment finished water. Seasonal variation is represented by the range column. No proprietary installation data was used in this dataset.

Why Ann Arbor water reads the way it does

Ann Arbor draws the majority of its water from the Huron River, with the remainder from a network of municipal wells. All supply is treated at the Barton Pond plant. The Huron River basin sits on glacial deposits over limestone bedrock. As groundwater percolates through that limestone it picks up dissolved calcium and magnesium carbonates, which is the chemistry behind hardness readings. The river concentrates and transports that mineral load to the intake.

The Barton Pond plant disinfects, removes turbidity, and stabilizes the corrosion chemistry of the finished water. It does not soften. EPA does not regulate hardness in drinking water because it is a nuisance issue rather than a health risk, so utilities have no federal compliance reason to remove it. The city publishes its annual Water Quality Report on a2gov.org each summer with the previous year's finished-water hardness, iron, and disinfectant residual numbers.

The practical result for an Ann Arbor homeowner is that hardness leaves the plant in the moderately hard to hard range and arrives at the tap roughly unchanged. A softener removes it. A whole-house carbon filter ahead of the softener handles the disinfectant residual, which is worth doing because chlorine and chloramine both degrade softener resin over time.

The PFAS situation in Ann Arbor source water

PFAS compounds have been detected in the Huron River since at least 2014. The source of contamination has not been definitively attributed. The City of Ann Arbor addresses this by running granular activated carbon (GAC) filtration specifically for PFAS removal, at an annual cost of approximately $250,000, and monitors 28 PFAS compounds. Current finished water meets all Michigan EGLE and EPA maximum contaminant levels. The Michigan EGLE Huron River PFAS response page tracks the ongoing monitoring program for the watershed.

One important clarification: a water softener does not remove PFAS. Ion exchange softeners target calcium and magnesium, not perfluorinated compounds. For PFAS reduction in drinking and cooking water, a reverse osmosis system certified to NSF/ANSI 58 is the residential standard. Most Ann Arbor homeowners we work with install both: the softener on the main water entry for the whole house, and an RO unit under the kitchen sink for drinking and cooking.

Sizing a softener from the Ann Arbor numbers

The Water Quality Association sizing methodology matches grain capacity to weekly grain load with roughly 25 percent regeneration headroom. Working from the Ann Arbor average of 7.4 GPG:

• A two-person household using 60 gallons per person per day generates roughly 6,200 weekly grains at 7.4 GPG. A 24,000 to 32,000 grain unit with weekly regeneration covers that.
• A four-person household at the same usage hits about 12,400 weekly grains. The 32,000 to 40,000 grain range handles it with headroom.
• If in-home testing shows readings at the high seasonal end (9 to 10.5 GPG), size up to 40,000 to 48,000 grain to maintain a reasonable regeneration interval.

These are starting frames. The in-home test we run before every install gives us the actual hardness reading, not a published average. Ann Arbor homes on private wells west and northwest of the city often read differently from city water.

Condition to action: matching the install to the house

When DIY makes sense, and when it does not

A handful of homeowners do install softeners themselves and end up with a working system. The cases where that goes well share a few things in common.

• The home is on city water, not a well, so iron and sulfur are not in play.
• The utility room has accessible copper or PEX plumbing with shutoff valves already in place.
• The homeowner has run an actual hardness test and is sizing from a number, not a guess.
• The drain run is short and meets local code for the air gap.

Call a professional if:

• You have galvanized iron plumbing or polybutylene that needs to be cut into.
• You are on a private well, even if a previous owner had a softener.
• You see staining, sulfur smell, or any iron reading above 0.3 mg/L on the test (the EPA Secondary MCL for iron).
• You want the install warranty and Washtenaw County permit paperwork handled.
• You are uncertain about grain capacity sizing and want the math validated against your actual hardness reading.

Frequently asked questions