Health Canada
Symbol of the Government of Canada

Common menu bar links

Environmental and Workplace Health

Guidelines For Canadian Drinking Water Quality - Supporting Documents - Hardness

1979

Help on accessing alternative formats, such as Portable Document Format (PDF), Microsoft Word and PowerPoint (PPT) files, can be obtained in the alternate format help section.

Table of Contents

Although hardness may have significant aesthetic effects, a maximum acceptable level has not been established because public acceptance of hardness may vary considerably according to the local conditions. Water supplies with a hardness greater than 200 mg/L are considered poor but have been tolerated by consumers; those in excess of 500 mg/L are unacceptable for most domestic purposes. Because water softening by sodium ion exchange may introduce undesirably high quantities of sodium into drinking water, it is recommended that where such a process is employed, a separate unsoftened supply be retained for drinking and culinary purposes.

General

Water hardness is a traditional measure of the capacity of water to react with soap. Hard water requires a considerable amount of soap to produce a lather, and it also leads to scaling of hot water pipes, boilers and other household appliances. Water hardness is caused by dissolved polyvalent metallic ions. In fresh waters, the principal hardness-causing ions are calcium and magnesium; strontium, iron, barium and manganese ions also contribute.Footnote 1 Hardness can be measured by the reaction of polyvalent metallic ions in a water sample with a chelating agent such as ethylenediaminetetra-acetic acid (EDTA) and is commonly expressed as an equivalent concentration of calcium carbonate.Footnote 1,Footnote 2 Hardness can also be estimated by determining the concentrations of the individual components of hardness and expressing their sum in terms of an equivalent quantity of calcium carbonate. The degree of hardness of drinking water may be classified in terms of its calcium carbonate concentration as follows: soft, 0 to <60 mg/L; medium hard, 60 to <120 mg/L; hard, 120 to < 180 mg/L; and very hard, 180 mg/L and above.Footnote 3,Footnote 5

Although hardness is caused by cations, it is often discussed in terms of carbonate (temporary) and non-carbonate (permanent) hardness.Footnote 4 Carbonate hardness refers to the amount of carbonates and bicarbonates that can be removed or precipitated from solution by boiling. This type of hardness is responsible for the deposition of scale in hot water pipes and tea kettles. Non-carbonate hardness is caused by the association of the hardness-causing cations with sulphates, chlorides and nitrates. It is also referred to as "permanent hardness" because it cannot be removed by boiling.

Alkalinity, an index of the buffering capacity of water, is closely linked to hardness. For the most part, alkalinity is produced by anions or molecular species of weak acids, mainly hydroxide, bicarbonate and carbonate; other species such as borates, phosphates, silicates and organic acids may also contribute to a small degree. Although numerous solute species may contribute to the alkalinity of water, alkalinity is expressed in terms of an equivalent quantity of calcium carbonate. As the alkalinity of most Canadian surface waters is due to the presence of carbonates and bicarbonates, their alkalinity is close to their hardness.Footnote 5

Sources and Levels of Hardness

The principal natural sources of hardness in water are sedimentary rocks and seepage and runoff from soils. In general, hard waters originate in areas with thick topsoil and limestone formations.Footnote 4 Groundwater is generally harder than surface water. Groundwater rich in carbonic acid and dissolved oxygen usually has a high solvating power; in contacting soil or rocks containing appreciable amounts of minerals, such as calcite, gypsum and dolomite, hardness levels up to several thousand milligrams per litre can result.Footnote 4,Footnote 6

The two main industrial sources of hardness are the inorganic chemical and mining industries.Footnote 4,Footnote 7 Industrial sources of calcium and magnesium have been briefly discussed in the calcium and magnesium reviews.

In a national survey of Canadian surface waters, conducted over the period 1975 to 1977, average hardness levels computed for each station were found to range as follows: British Columbia, 7 to 180 mg/L; Northwest Territories, 5 to 179 mg/L; Alberta, 98 to 329 mg/L; Saskatchewan, 12 to 132 mg/L; and Manitoba, 15 to 716 mg/L. Hardness levels in the Maritime provinces were not monitored.Footnote 8 Waters in the upper Great Lakes had hardness levels ranging from 40 to 80 mg/L.Footnote 9 Ontario lakes and streams showed a very broad range in hardness levels; levels from 2 to 1803 mg/L were reported, but most were between 40 and 200 mg/L.Footnote 10 In a review of national water quality, 41 locations were chosen as representative of Canadian waters. The median of the values measured at each station rarely exceeded 120 mg/L, except in the Nelson-Saskatchewan and Mississippi basins. The waters of these river systems are considered to be hard, as most hardness levels exceed 180 mg/L. None of the median concentrations for these 41 stations exceeded 500 mg/L.Footnote 3

A survey of municipal water supplies in Canada showed that half of all Canadian municipalities had hardness levels below 80 mg/L, and 20% had levels greater than 180 mg/L.Footnote 11 Only in the Prairie provinces and Ontario did levels appreciably exceed 180 mg/L. In Ontario, the hardness of drinking water from surface sources ranged from 3.7 to 296 mg/L, with an average of 95 mg/L; the hardness of groundwater supplies was higher, and levels ranged from 40 to 1300 mg/L, with an average of 294 mg/L.Footnote 12,Footnote 13 In a recent survey of 525 municipalities throughout Canada, only 17 cities had drinking water hardness levels above 500 mg/L.Footnote 14 These cities were in Ontario and Saskatchewan.

Health Considerations

The cations that are the major contributors to hardness -- calcium and magnesium -- are not of direct public health concern. These parameters are discussed further in separate reviews.

A number of epidemiological investigations, including ones in Canada,Footnote 11,Footnote 15,Footnote 16 England,Footnote 17-Footnote 24 AustraliaFootnote 25 and the United States,Footnote 26-Footnote 30 have suggested that there is an inverse statistical correlation between drinking water hardness and certain types of cardiovascular disease. Other workers Footnote 1,Footnote 31-Footnote 35 have reported that significant correlations cannot be demonstrated. No conclusions can be made, therefore.

A number of other studies have been undertaken to determine if there are any relationships between drinking water hardness and other diseases, including cancer.Footnote 21,Footnote 23,Footnote 26,Footnote 29,Footnote 34 Again, inverse correlations have been reported, but the significance of these data is debatable.

Domestic water supplies are often softened by the addition of lime and soda ash or the use of ion exchange zeolite. Water softening can result in the addition of high levels of sodium to the water,Footnote 20 particularly where certain ion exchange processes are employed. Although a direct relationship between sodium and hypertension has not been established in humans (see review of sodium), it is considered advisable to avoid the unnecessary addition of sodium to drinking water. A World Health Organization working group on sodium in drinking water has recently recommended that "trends towards unnecessary sodium in water supplies should be discouraged."Footnote 36 It is therefore recommended that where water softening by ion exchange is considered necessary, a separate unsoftened water supply be retained for drinking and culinary purposes.

Other Considerations

Soft water can lead to corrosion of pipes,Footnote 30,Footnote 37 and, consequently, certain heavy metals such as copper, zinc, lead and cadmium may be present in the distributed water.Footnote 38-Footnote 41 The degree to which this occurs is also a function of pH, alkalinity and dissolved oxygen concentration (see also review of pH). In some communities, corrosion is so severe that the water must be treated.Footnote 42

In areas with hard water, household pipes can become clogged with scale;Footnote 43 hard waters also cause incrustations on kitchen utensils and increase soap consumption. Hard water is thus both a nuisance and an economic burden to the consumer. Public acceptance of hardness varies among communities; it is often related to the hardness to which the consumer has become accustomed, and in many communities hardness greater than 200 mg/L is tolerated. It has been suggested that a hardness level of 80 to 100 mg/L (as CaCO3) provides an acceptable balance between corrosion and incrustation.Footnote 44

Conclusion

  1. Hard water causes incrustation in distribution systems and excessive soap consumption; soft water may result in corrosion of water pipes. Public acceptability of the degree of hardness may vary considerably from community to community depending on local conditions. Therefore, a maximum acceptable level for hardness cannot be specified.
  2. Hardness levels between 80 and 100 mg/L (as CaCO3) are generally considered to provide an acceptable balance between corrosion and incrustation. Waters with hardness levels in excess of 200 mg/L are considered poor but have been tolerated by consumers. Waters with hardness in excess of 500 mg/L are unacceptable for most domestic purposes.

Recommendation

Where softening by ion exchange is considered necessary, it is recommended that a separate unsoftened water supply be retained for drinking and culinary purposes.

References

Footnote 1

U.S. Environmental Protection Agency. Quality criteria for water. Office of Water and Hazardous Materials Rep. EPA-440/9-76-023, Washington, DC, July (1976).

Return to the first footnote 1 referrer

Footnote 2

Sekerka, I. and Lechner, J.F. Simultaneous determination of total non-carbonate and carbonate water hardness by direct potentiometry. Talanta, 22: 459 (1975).

Return to the first footnote 2 referrer

Footnote 3

Environment Canada. Surface water quality in Canada -- an overview. Water Quality Branch, Inland Waters Directorate (1977).

Return to the first footnote 3 referrer

Footnote 4

Sawyer, C.N. and McCarty, P.L. Chemistry for sanitary engineers. 2nd edition. McGraw-Hill Series in Sanitary Science and Water Resources Engineering, McGraw-Hill, Toronto (1967).

Return to the first footnote 4 referrer

Footnote 5

Thomas, J.F.J. Industrial water resources of Canada. Water Survey Rep. No. 1. Scope, procedure, and interpretation of survey studies. Queen's Printer, Ottawa (1953).

Return to the first footnote 5 referrer

Footnote 6

De Fulvio, S. and Olori, L. Definitions and classification of naturally soft and naturally hard waters. Chemical and physical characteristics of the water in some member states of the European community. In: Hardness of drinking water and public health. Proceedings of the European Scientific Colloquium, Luxembourg, 1975. R. Amavis, W.J. Hunter and J.G.P.M. Smeets (eds.). Pergamon for the Commission of the European Communities, New York, NY. p.95 (1976).

Return to the first footnote 6 referrer

Footnote 7

Biesecker, J.E. and George, J.R. Stream quality in Appalachia as related to coal-mine drainage, 1965. In: Water quality in a stressed environment: readings in environmental hydrology. W.A. Pettyjohn (ed.). Burgess Publishing Company, Minneapolis, MN (1972).

Return to the first footnote 7 referrer

Footnote 8

National Water Quality Data Bank. Inland Waters Directorate, Water Quality Branch, Environment Canada (1977).

Return to the first footnote 8 referrer

Footnote 9

Upper Lakes Reference Group. The waters of Lake Huron and Lake Superior. Vol. 1. Summary and recommendations. Report to the International Joint Commission (1977).

Return to the first footnote 9 referrer

Footnote 10

Ontario Ministry of the Environment. Water quality data, Ontario lakes and streams 1974. Vol. IX. Water Resources Branch (1974).

Return to the first footnote 10 referrer

Footnote 11

Neri, L.C., Hewitt, D. and Mandel, J.S. Relation between mortality and water hardness in Canada. Lancet, i: 931 (1972).

Return to the first footnote 11 referrer

Footnote 12

Overment, W. (ed.). 1977/78 directory and environmental handbook. Water Pollut. Control, 115: 10 (1977).

Return to the first footnote 12 referrer

Footnote 13

Ontario Ministry of the Environment. Operating summary, water supply systems 1976. Municipal and Private Section, Pollution Control Branch (1976).

Return to the first footnote 13 referrer

Footnote 14

Johansen, H. Personal communication. Bureau of Epidemiology, Health and Welfare Canada.

Return to the first footnote 14 referrer

Footnote 15

Anderson, T.W., Neri, L.C., Schreiber, G.B., Talbot, F.D.F. and Zdrojewski, A. Ischemic heart disease, water hardness and myocardial magnesium. J. Can. Med. Assoc., 113: 199 (1975).

Return to the first footnote 15 referrer

Footnote 16

Anderson, T.W., Riche, W.H. and MacKay, J.S. Sudden death and ischemic heart disease. New Engl. J. Med., 280(15): 805 (1969).

Return to the first footnote 16 referrer

Footnote 17

Crawford, T. and Crawford, M.D. Prevalence and pathological changes of ischaemic heart-disease in a hard-water and in a soft-water area. Lancet, i: 7484 (1967).

Return to the first footnote 17 referrer

Footnote 18

Shaper, A.G., Clayton, D.G. and Morris, J.N. The hardness of water supplies and cardiovascular disease. Proceedings of the International Water Supply Association, Brighton, U.K. (1974), cited in reference 30.

Return to the first footnote 18 referrer

Footnote 19

Shaper, A.G. Water hardness and cardiovascular disease. Water Research Centre, Medmenham, U.K. (1975), cited in reference 30.

Return to the first footnote 19 referrer

Footnote 20

Crawford, M.D. Hardness of drinking water and cardiovascular disease. Proc. Nutr. Soc., 31(3): 346 (1972).

Return to the first footnote 20 referrer

Footnote 21

McCabe, L.J. The correlation of drinking water quality and vascular disease. Paper presented at the Conference on Cardiovascular Disease Epidemiology, Chicago, IL, February (1963), cited in reference 39.

Return to the first footnote 21 referrer

Footnote 22

Crawford, M., Clayton, D.G., Stanley, F. and Shaper, A.G. An epidemiological study of sudden death in hard and soft water areas. J. Chronic Dis., 30: 69 (1977).

Return to the first footnote 22 referrer

Footnote 23

Crawford, M., Gardner, M.J. and Morris, J.N. Mortality and hardness of local water supplies. Lancet, i: 827 (1968).

Return to the first footnote 23 referrer

Footnote 24

Stitt, F.W., Crawford, M.D., Clayton, D.G. and Morris, J.N. Clinical and biochemical indicators among men living in hard and soft water areas. Lancet, i: 122 (1973).

Return to the first footnote 24 referrer

Footnote 25

Lyster, W.R. The records of Brisbane water supply and seasonality in local deaths. Int. J. Environ. Stud., 3: 329 (1972).

Return to the first footnote 25 referrer

Footnote 26

Schroeder, H.A. Relation between mortality from cardiovascular disease and treated water supplies. Variation in states and 163 largest municipalities. J. Am. Med. Assoc., 172: 1902 (1960).

Return to the first footnote 26 referrer

Footnote 27

Schroeder, H.A. Municipal drinking water and cardiovascular death rates. J. Am. Med. Assoc., 195: 125 (1966).

Return to the first footnote 27 referrer

Footnote 28

Voors, A.W. Minerals in municipal water and atherosclerotic heart death. Am. J. Epidemiol., 93: 259 (1970).

Return to the first footnote 28 referrer

Footnote 29

Sauer, H.I. Relationship between trace element content of the drinking water and chronic diseases, observed effects of trace elements in drinking water on human health. Presented at the 16th Water Quality Conference, University of Illinois, Urbana, IL (1974), cited in reference 39.

Return to the first footnote 29 referrer

Footnote 30

Hudson, H.E., Jr., and Gilcreas, F.W. Health and economic aspects of water hardness and corrosiveness. J. Am. Water Works Assoc., 68: 201 (1976).

Return to the first footnote 30 referrer

Footnote 31

Allwright, S.P.A., Coulson, A. and Detels, R. Mortality and water hardness in three matched communities in Los Angeles. Lancet, ii: 860 (1974).

Return to the first footnote 31 referrer

Footnote 32

Comstock, G.W. Fatal arteriosclerotic heart disease, water hardness at home, and socioeconomic characteristics. Am. J. Epidemiol., 94: 1 (1971).

Return to the first footnote 32 referrer

Footnote 33

Tuthill, R.W. Explaining variations in cardiovascular disease mortality within a soft water area. Office of Water Research and Technology, Division of Public Health, U.S. Department of Commerce, U7710 PB-263 482/2S1 (1976).

Return to the first footnote 33 referrer

Footnote 34

Stocks, P. Mortality from cancer and cardiovascular disease in the country boroughs of England and Wales classified according to sources and hardness of their water supplies, 1958-1967. J. Hyg., 71: 237 (1973).

Return to the first footnote 34 referrer

Footnote 35

Meyers, D. Mortality and water hardness. Lancet, i: 398 (1975).

Return to the first footnote 35 referrer

Footnote 36

World Health Organization. Summary report of the Working Group on Sodium, Chlorides, and Conductivity in Drinking Water. The Hague (1978).

Return to the first footnote 36 referrer

Footnote 37

Larson, T.E. Deterioration of water quality in distribution systems. J. Am. Water Works Assoc., 58: 1307 (1966).

Return to the first footnote 37 referrer

Footnote 38

Neri, L.C. Some data from Canada. In: Hardness of drinking water and public health. Proceedings of the European Scientific Colloquium, Luxembourg, 1975. R. Amavis, W.J. Hunter and J.G.P.M. Smeets (eds.). Pergamon for the Commission of the European Communities, New York, NY. p. 343 (1976).

Return to the first footnote 38 referrer

Footnote 39

Sharrett, A.R. and Feinleib, M. Water constituents and trace elements in relation to cardiovascular diseases. Prev. Med., 4: 20 (1975).

Return to the first footnote 39 referrer

Footnote 40

Craun, G.F. and McCabe, L.J. Problems associated with metals in drinking water. J. Am. Water Works Assoc., 67: 593 (1975).

Return to the first footnote 40 referrer

Footnote 41

Neri, L.C. and Hewitt, D. Review and implications of ongoing and projected research outside the European communities. In: Hardness of drinking water and public health. Proceedings of the European Scientific Colloquium, Luxembourg, 1975. R. Amavis, W.J. Hunter and J.G.P.M. Smeets (eds.). Pergamon for the Commission of the European Communities, New York, NY. p. 443 (1976).

Return to the first footnote 41 referrer

Footnote 42

Mullen, E.D. and Ritter, J.A. Potable-water corrosion control. J. Am. Water Works Assoc., 66: 473 (1974).

Return to the first footnote 42 referrer

Footnote 43

Coleman, R.L. Potential public health aspects of trace elements and drinking water quality. Ann. Okla. Acad. Sci., 5: 57 (1976).

Return to the first footnote 43 referrer

Footnote 44

Bean, E.L. Quality goals for potable water. J. Am. Water Works Assoc., 60: 1317 (1968).

Return to the first footnote 44 referrer