Hard water, explained
Hard water is tap water with a lot of dissolved calcium and magnesium. It is measured in milligrams per litre or grains per gallon, and the higher the number, the more scale it leaves on kettles, fixtures, and water heaters. It is safe to drink. Here is what the number means, and how to find yours.
Find your town's water hardness
Type an Ontario town or postal code for its published figure in mg/L and grains per gallon, with the source and the date it was checked.
Find your water hardness
Enter a town name or the first three postal-code characters.
How is water hardness measured?
Water hardness is the amount of dissolved calcium and magnesium, given in milligrams per litre as calcium carbonate (mg/L) or in grains per gallon (gpg). One grain per gallon is about 17.1 mg/L. Utility reports usually use mg/L; home test kits and softeners are set in grains. The bands below run from soft to very hard.
What does hard water do in your home?
Hard water leaves scale: a chalky buildup inside kettles, coffee makers, showerheads, and water heaters that shortens their life and cuts their efficiency. It makes soap lather less, spots glassware, and can leave a film on skin. None of this is a health problem. It is a wear-and-cost problem, and it gets worse the higher the number.
Is hard water safe to drink?
Yes. Health Canada sets no health-based limit on hardness, because the calcium and magnesium that make water hard are dietary minerals, not contaminants. Very hard water can taste mineral and is tough on plumbing, but it is safe. The one thing to watch is softened water, which trades that hardness for a little added sodium.
Do you need a water softener?
It depends on the number. Soft and moderately hard supplies rarely need one. Hard and very hard water leaves enough scale that a softener usually pays for itself in appliance life, and it is the norm in groundwater cities such as Guelph, Kitchener, and Waterloo. Test your own tap before you buy or size one.
Hard water questions
What is water hardness measured in?
Milligrams per litre as calcium carbonate (mg/L) or grains per gallon (gpg). One grain per gallon is about 17.1 mg/L.
Is hard water bad for your hair or skin?
It can leave a soap film and make hair feel rougher, but it does not damage skin or hair and is not a health risk. A rinse or a showerhead filter helps if it bothers you.
Does boiling water remove hardness?
Boiling drops some temporary hardness out as scale, which is why kettles fur up, but it does not soften water for the house. Only a softener or certain filters do that.
Which Ontario cities have the hardest water?
Groundwater communities such as Guelph, Kitchener, Waterloo, and Cambridge are the verified very-hard standouts. Great Lakes systems like Toronto and Hamilton sit in the moderate band.
Sources
Hardness guidance from Health Canada drinking-water operational parameters. Municipal figures are each city's own published values, last checked 2026-06-24. Hardness varies by neighbourhood, season, and which well or plant serves your street, especially on groundwater systems. These are the municipal published figures as of the verified date, good for planning, not a substitute for a home test or your utility's current report.
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