Windsor Water Is Hard — Here's What It Costs You Each Year

Why Is Windsor Water So Hard?

Windsor sits at the southwestern tip of Ontario, right where the Detroit River funnels water out of Lake St. Clair and into Lake Erie. Your water comes from the Windsor Utilities Commission, which draws from both lakes, and that’s the whole story behind the hardness. These are not mountain streams running over granite. They are shallow, warm, biologically rich lakes sitting on a bed of limestone and dolomite, the same carbonate bedrock that underlies most of the Great Lakes basin.

Here’s how it works. Rain and snowmelt seep through the soil and into the limestone bedrock. Limestone is essentially fossilized calcium carbonate, and dolomite adds magnesium carbonate to the mix. As the water moves through that rock, it slowly dissolves the carbonates. It’s a chemical reaction that’s been running for thousands of years, and it loads the water with dissolved calcium and magnesium ions. That’s hardness. It’s not a contaminant and it’s not pollution; it’s just the natural result of water doing what water does to soluble rock.

Lake St. Clair is the shallowest lake in the Great Lakes system, averaging only about 11 feet deep. Shallow water stays warmer, and warmer water holds more dissolved carbon dioxide. That extra CO2 makes the water slightly more acidic, which in turn makes it even better at dissolving limestone. So you get a double whammy: the bedrock is rich in calcium and magnesium, and the shallow, warm conditions speed up the dissolution. By the time that water reaches your tap, it’s sitting at 9.8 grains per gallon, or 168 parts per million. That puts it squarely in the “hard” category, just a hair below the 10.5 GPG threshold where the USGS would call it “very hard.”

The EPA doesn’t regulate hardness as a health hazard. It’s purely aesthetic, covered under a Secondary Maximum Contaminant Level. That means the water is perfectly safe to drink; the hardness is about what it does to your pipes, your water heater, and your soap, not your health.

How Windsor Compares to Nearby Cities

Windsor’s hardness is typical for the region, and here’s why: your neighbors are drinking from the same geological tap. Detroit sits directly across the Detroit River and draws its water from Lake Huron via the Detroit River, but that water passes through the same carbonate-rich bedrock and ends up in the same hardness ballpark. The USGS classifies water above 7 GPG as hard and above 10.5 GPG as very hard, and most of the Great Lakes shoreline falls somewhere in that range.

London, Ontario, is the outlier in this group. It draws from the Thames River and from deep groundwater wells in the same limestone and dolomite formations, but groundwater tends to have more contact time with the rock, so it often comes out harder than surface water. If you’ve ever noticed London water feeling a bit slicker or leaving more spots on glasses, you’re not imagining it.

Sarnia and Leamington are closer cousins to Windsor. Sarnia sits on Lake Huron, which is deeper and colder than Lake St. Clair, and colder water holds less dissolved CO2, so it dissolves less limestone. That usually means slightly lower hardness than Windsor, but not dramatically so. Leamington, on the other hand, is right on Lake Erie’s north shore and shares Windsor’s shallow, warm-water conditions. Its hardness runs close to yours, and it faces the same scale buildup in kettles and water heaters.

Here’s the practical difference. At 9.8 GPG, your water is hard enough that you’re probably seeing scale on faucets and showerheads, and your laundry might feel stiff no matter how much detergent you use. The WQA and Battelle Memorial Institute found in a 2010 study that soft water can cut laundry detergent use by up to 50% and dish soap by up to 70%. And the WQRF estimates hard water costs the average affected household around $800 a year in energy, premature appliance wear, and extra cleaning products. That’s not a scare tactic; that’s just the math of running a household on hard water.

Your neighbors in Detroit and Leamington are dealing with the same reality. London might have it slightly worse depending on which well is feeding the system. Sarnia might get a small break from the deeper, colder lake water. But none of them are escaping the limestone. It’s the bedrock of the entire region, and it’s in every glass of water from Windsor to Cleveland.

How does Windsor stack up against the rest of Ontario? It's hard at 9.8 GPG — Guelph, Thunder Bay, and Barrie sit nearby with different numbers. See the full hardest-water ranking for context.

Want the broader explainer on what hardness actually is and how it behaves? Read hard water vs. soft water, explained.