Quebec

Montréal water hardness

The Atwater and Charles-J.-Des Baillets plants supply Montréal, Montréal-Ouest and Mont-Royal with water from the St. Lawrence. In 2024, total hardness on that network averaged 117 mg/L, from 109 to 126 mg/L. That is moderately hard water, close to the 120 mg/L line where hard water starts, and about twice as hard as Laval's. West Island plants publish separate results that we have not verified yet, so this page does not cover them.

Data last reviewed October 17, 2026.

What this means for your appliances

Moderately hard

Some scale builds up over time, mostly where water gets heated: kettles, coffee makers and washers. A monthly clean keeps it in check.

Recommended for your water

Dishwasher Cleaner

5.0(15)

Dissolves grease, detergent residue and limescale buildup, and removes odour-causing buildup.

Clears grease, limescale and odour buildup

$23.95

Washing Machine Cleaner

4.9(14)

Breaks down residue and odour-causing buildup inside your washer.

Removes odour and buildup from the drum and hoses

$24.95

Coffee Maker Cleaner

4.8(14)

Removes limescale, mineral buildup and coffee oils inside your coffee maker.

Descales for better-tasting coffee

$24.95

Guides for hard water

What counts as hard water?

We use the U.S. Geological Survey scale, in mg/L as CaCO₃.

  • Soft 0 to 60 mg/L
  • Moderately hard 61 to 120 mg/L
  • Hard 121 to 180 mg/L
  • Very hard Over 180 mg/L

How to read the units

Utilities usually report hardness in mg/L as calcium carbonate (CaCO₃), which is the same as ppm. Dishwasher and softener manuals often use grains per gallon or German degrees instead. Here is how they convert:

  • 1 US grain per gallon = 17.1 mg/L
  • 1 imperial grain per gallon = 14.25 mg/L
  • 1 °dH = 17.85 mg/L
  • 1 mmol/L = 100.09 mg/L

Questions and answers

Is Montréal water hard?

Moderately hard, close to the line. On the Atwater and Charles-J.-Des Baillets network, total hardness averaged 117 mg/L in 2024, from 109 to 126 mg/L. Water counts as hard above 120 mg/L, so some samples crossed it.

Is Montréal's water harder than Laval's?

Yes. Montréal's network averaged 117 mg/L in 2024, while Laval's three plants averaged 50 to 61 mg/L in 2025. The St. Lawrence water on the island is about twice as hard as the river water Laval treats.

Does this cover the West Island?

No. Pierrefonds, Pointe-Claire, Dorval and Lachine have their own plants. We will add them once we have verified their published results.

What is Montréal's water hardness in grains per gallon?

Atwater and Charles-J.-Des Baillets plants: 6.8 grains per US gallon, or 8.2 grains per imperial gallon.

Where do these numbers come from?

Ville de Montréal, 2024 annual drinking water report for Montréal, Montréal-Ouest and Mont-Royal (PDF, in French). Data for 2024, annual report. We update this page when a new report comes out.

Sources

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