Ontario

Guelph water hardness

Guelph's tap water measures 21 to 33 grains per US gallon, or about 359 to 564 mg/L. Along with Kitchener-Waterloo, that makes it some of the hardest city water in Canada.

Data last reviewed October 17, 2026.

City of Guelph

359 to 564 mg/L as CaCO₃ Very hard
  • Published range
  • 21 to 33 gpg (US)

In other units

US grains per gallon
21.0 to 33.0
Imperial grains per gallon
25.2 to 39.6
German degrees (°dH)
20.1 to 31.6
Millimoles per litre
3.59 to 5.64

Source: Region of Waterloo and City of Guelph (Water Softener Facts), My water hardness. Data for: Range published by the source, no date given. Checked October 15, 2026.

What this means for your appliances

Very hard

Scale builds fast. Descale your coffee maker and ice machine often, and clean the dishwasher and the washer about every two weeks.

Recommended for your water

Coffee Maker Cleaner

4.8(14)

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

Descales for better-tasting coffee

$24.95

Ice Machine Cleaner

4.9(13)

Removes mineral buildup and odours inside your ice machine.

Descales and freshens countertop ice makers

$24.95

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

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

How hard is Guelph water?

Very hard: 21 to 33 grains per US gallon, or about 359 to 564 mg/L.

Do I still need to clean my appliances if I have a water softener?

A softener reduces hardness, so less scale builds up where softened water reaches. Your dishwasher and washer still collect grease, detergent residue and odours, so cleaning the dishwasher and the washer about every two weeks still makes sense.

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

City of Guelph: 21.0 to 33.0 grains per US gallon, or 25.2 to 39.6 grains per imperial gallon.

Where do these numbers come from?

Region of Waterloo and City of Guelph (Water Softener Facts), My water hardness. Data for Range published by the source, no date given. We update this page when a new report comes out.

Sources

Check another city