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Water hardness

Learn more about water hardness, including the difference between hard and soft water, how water hardness affects dishwashers and washing machines, and the water hardness ratings for different parts of Calgary.

To learn more about where Calgary gets its drinking water and see answers to other drinking water-related questions, visit water supply and drinking water.

What is water hardness?

Water hardness is caused by calcium and magnesium in the ground and surface water. If either of these minerals are present in your drinking water in high concentrations, the water is considered hard. These minerals come from rock such as limestone that dissolves in our river system. The result of hard water is difficulty making lather or suds for washing and a build-up of minerals on taps and other fixtures.

Water containing low concentrations of calcium or magnesium is called soft water. Municipalities with soft drinking water often have higher incidences of water pipe corrosion (low pH). The degree of hardness in drinking water is commonly classified in terms of its concentration of calcium carbonate:

Hardness rating

Concentration of Calcium Carbonate (mg/L)

Concentration of Calcium Carbonate (grains/ imperial gallon)

Soft

0 to <75 0 to <5.2

Medium hard

75 to <150 5.2 to <10.5

Hard

150 to <300 10.5 to <21

Very hard

300 and greater 21 and greater

Are there health issues with water hardness?

There are no known health effects associated with calcium and magnesium minerals in drinking water. However, conventional water softening systems (those that use salts) may not be suitable for people on sodium-reduced diets.

We recommend that consumers thoroughly research the various water softener systems available before deciding whether or not to soften their water. Also, water softeners should be connected so that the water you are drinking is not softened.

Can water hardness affect dishwashers and washing machines?

Hard water can reduce the effectiveness of detergent. Hard water may also cause automatic dishwashers or washing machines to leave film on dishes or leave residue on clothing, and can also cause mineral build-up on mechanical parts.

The easiest solution to hard water problems is to increase the amount of detergent used in proportion to the degree of water hardness. Check with your appliance user manual or the manufacturer for instructions.

How do water softeners work?

Water softeners replace the non-toxic hard minerals with sodium or potassium. The amounts added are relatively insignificant compared to what you ingest from your food. They should not pose health problems, unless you are on a salt-reduced diet.

Most water softeners regenerate with salt and water. Regeneration is a process where the softening materials (called resins) inside the softener can be used over and over again. Once regeneration is completed, the salt and water solution is flushed into the sewer and into the environment. A correctly operating water softener will use salt and water efficiently, saving you money while reducing the impact on the environment.

How do I regenerate my water softener?

Water softeners must regenerate frequently using salt and water. How often a water softener must regenerate depends on the hardness of your drinking water supply. Water softener manufacturers often classify hardness of the water supply using the unit grains per Imperial gallon.

How hard is Calgary's water?

The hardness of Calgary's water varies seasonally and by location:

  • The lowest hardness levels are typically during spring snowmelt and the highest hardness levels are between December and February.
  • The Bow and Elbow Rivers each have different hardness levels and provide water to different parts of the city.

Generally, people in the northern half of the city receive water from the Bow River through the Bearspaw Water Treatment Plant. Residents in the south receive most of their water from the Elbow River through the Glenmore Water Treatment Plant.

Residents in both halves of Calgary may receive a mix of water from both treatment plants, depending on flow conditions and city water demand.

What is the hardness rating in north Calgary?

The table shows the monthly values for water hardness as expressed as Calcium carbonate CaCO3 in both milligrams per litre (mg/L) and grains per imperial gallon.

Bearspaw Treatment Plant Effluent Water Hardness (mg CaCO3) for 2015

Month

mg/L CaCO 3

grains/gallon

January

186 13.0

February

182 12.7

March

178 12.5

April

173 12.1

May

174 12.2

June

140 9.8

July

143 10.0

August

150 10.5

September

156 10.9

October

157 11.0

November

170 11.9

December

182 12.8

Average

165.9 11.6

What is the hardness rating in south Calgary?

The table shows the monthly values for water hardness as expressed as Calcium carbonate CaCO3 in both milligrams per litre (mg/L) and grains per imperial gallon.

Glenmore Treatment Plant Effluent Water Hardness (mg CaCO3) for 2015

Month

mg/L CaCO 3

grains/gallon

January

238 16.7

February

232 16.2

March

228 15.9

April

200 14.0

May

211 14.8

June

201 14.0

July

195 13.6

August

194 13.5

September

205 14.3

October

220 15.4

November

227 15.9

December

237 16.6

Average

215.7 15.1