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

Why Is Markham Water So Hard?

Markham gets its water from Lake Ontario, drawn and treated by York Region. That’s surface water, not groundwater, and it’s a crucial detail for understanding why your water sits at 7.4 GPG (126 ppm), which puts it squarely in the “hard” category.

Here’s the thing about the Great Lakes: they’re not some pristine mountain spring. Lake Ontario drains a massive watershed, and every river and stream feeding it runs over and through the surrounding terrain. That terrain is rich in limestone and dolomite, sedimentary rocks made largely of calcium and magnesium carbonate. Rainwater, slightly acidic from dissolved carbon dioxide, slowly dissolves these rocks as it travels. The calcium and magnesium ions hitch a ride downstream, and they end up concentrated in the lake itself.

Ontario’s geology is practically a textbook example of this. The region sits on a foundation of Paleozoic sedimentary rock, with thick layers of limestone and dolomite laid down hundreds of millions of years ago when this area was a shallow tropical sea. The Niagara Escarpment, which runs through southern Ontario, is essentially a giant exposed slab of dolomite and limestone. Every drop of water that flows off that escarpment and into the lake picks up dissolved minerals along the way. By the time it reaches the intake pipes at York Region’s treatment plants, the water has a naturally elevated mineral load. The treatment process removes sediment and pathogens, but it doesn’t strip out calcium and magnesium. That’s not a failure of the utility; it’s simply not what municipal treatment is designed to do.

So when you fill a glass in Markham, you’re drinking water that has essentially been steeping in limestone for a long time. That’s the whole story. It’s not contamination, and it’s not a treatment plant problem. It’s geology, plain and simple.

How Markham Compares to Nearby Cities

If you live in Markham and your water is hard, here’s the thing: your neighbours are in the same boat. York Region operates a connected municipal system, and most communities in the area draw from the same source. Lake Ontario is the shared tap for a huge swath of the Greater Toronto Area. That means the water in Markham is fundamentally the same water that comes out of taps in Richmond Hill, Vaughan, Aurora, and Newmarket, all of which are supplied by York Region’s distribution network.

That’s not to say every municipality in the region is identical. Some towns further north, like parts of King Township or Georgina, may supplement with groundwater wells, and those wells can tap into deeper aquifers with different mineral profiles. Groundwater in this part of Ontario often runs even harder than lake water because it has more contact time with the limestone bedrock. But for the core York Region communities that rely on Lake Ontario, you’re looking at a consistent water chemistry across the board.

The USGS classifies water above 7 GPG as hard and above 10.5 GPG as very hard. At 7.4 GPG, Markham sits just above the threshold, and it’s right in line with the US national average of about 7.3 GPG. So while your water is technically hard, it’s not extreme. It’s typical for the Great Lakes region, and it’s typical for the country as a whole. Roughly 85% of US households deal with hard water, according to USGS, so Markham is far from an outlier.

What does that mean practically? The EPA doesn’t regulate hardness as a health hazard; it’s purely an aesthetic and nuisance issue. But it does have real effects on your home. Battelle Memorial Institute and WQRF research from 2009 found that hard water causes about a 4% efficiency loss in gas water heaters per 5 GPG of hardness. The Department of Energy notes that just a quarter-inch of scale buildup can cut water heater efficiency by up to 40%. And a 2010 WQA/Battelle study showed you can use up to 50% less laundry detergent and 70% less dish soap with soft water. Based on the WQA-commissioned Battelle Memorial Institute study, hard water is estimated to cost the average affected household more each year in extra energy, premature appliance wear, and additional cleaning products — see the cost calculator on this page for the number scaled to this city’s actual hardness. It’s the limestone talking. And it’s the same story for most of your neighbours in York Region.

How does Markham stack up against the rest of Ontario? It's hard at 7.4 GPG — Woodstock, Guelph, and Ingersoll sit nearby with different numbers. See the full hardest-water ranking for context.

See where Markham sits on the Ontario water hardness map →

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