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Total Dissolved Solids (TDS)
September 1978
(Updated January 1991)
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(PDF Version - 27 K)Table of Contents
- Total Dissolved Solids (TDS)
- Definition
- Occurrence
- Analytical Methods and Treatment Technology
- Health Considerations
- Other Considerations
- Rationale
- References
Total Dissolved Solids (TDS)
An aesthetic objective of ≤500 mg/L has been established for total dissolved solids (TDS) in drinking water. At higher levels, excessive hardness, unpalatability, mineral deposition and corrosion may occur. At low levels, however, TDS contributes to the palatability of water.
Definition
Total dissolved solids (TDS) comprise inorganic salts and small amounts of organic matter that are dissolved in water. The principal constituents are usually the cations calcium, magnesium, sodium and potassium and the anions carbonate, bicarbonate, chloride, sulphate and, particularly in groundwater, nitrate (from agricultural use).
Occurrence
Total dissolved solids in water supplies originate from natural sources, sewage, urban and agricultural runoff and industrial wastewater. In Canada, salts used for road deicing can contribute significantly to the TDS loading of water supplies. Concentrations of TDS in water vary owing to different mineral solubilities in different geological regions. The concentration of TDS in water in contact with granite, siliceous sand, well-leached soil or other relatively insoluble materials is usually below 30 mg/L.Footnote 11 In areas of Precambrian rock, TDS concentrations in water are generally less than 65 mg/L.Footnote 22 Levels are higher in regions of Palaeozoic and Mesozoic sedimentary rock, ranging from 195 to 1100 mg/LFootnote 22 because of the presence of carbonates, chlorides, calcium, magnesium and sulphates.Footnote 11,Footnote 33Concentrations of TDS in some streams and small lakes in the arid western regions of Canada and the United States are often as high as 15 000 mg/L.Footnote 33,Footnote 44Concentrations of TDS, expressed as the sum of its constituents, were below 500 mg/L in 36 of 41 rivers monitored in Canada.Footnote 55 In a survey of the Great Lakes, TDS levels ranged from 61 to 227 mg/L.Footnote 66 The levels of TDS in all of the Great Lakes except Lake Superior increased between 1900 and 1970. A threefold increase in chlorides and a twofold increase in sulphates, sodium and potassium in Lakes Erie and OntarioFootnote 77 increased the TDS concentration in those lakes by 50 to 60 mg/L.Footnote 66,Footnote 8
Concentrations of TDS in drinking water in Canada are generally below 500 mg/L but are considerably higher in some locations, particularly the arid western regions. Levels of TDS in Newfoundland and Labrador were below 500 mg/L in 96% of 103 communities sampled from 1969 to 1989 (range 10 to 2263 mg/L; average 146 mg/L).Footnote 1111 In Quebec, samples of distributed water taken at 19 plants between 1987 and 1989 contained TDS at mean concentrations ranging from 58 to 213 mg/L.Footnote 1212 Concentrations of TDS in distributed water from 31 plants in Ontario during 1987 and 1988 ranged from 91 to 470 mg/L.Footnote 1313 In Manitoba, TDS concentrations measured during 1988 in the treated water of 168 communities ranged from 56 to 2510 mg/L; concentrations were less than 500 mg/L in 19% of these communities.Footnote 1414 Levels of TDS in 1978 samples of community drinking water taken between 1970 and 1989 in Saskatchewan ranged from 6.5 to 5376 mg/L.Footnote 1515 Concentrations of TDS in 54% of 1042 communities surveyed in Alberta in October 1989 were below 500 mg/L (range <100 to 1000 mg/L).Footnote 1616 In British Columbia, concentrations of TDS in individual well water supplies ranged from 120 to 4662 mg/L; those in community (generally surface water) supplies were commonly less than 500 mg/L.Footnote 1717
Analytical Methods and Treatment Technology
The method most commonly used for the analysis of TDS in water supplies is the measurement of specific conductivity with a conductivity probe that detects the presence of ions in water. Conductivity measurements are converted to TDS values by a factor that varies with the type of water.Footnote 1818,Footnote 1919 The practical quantitation limit for TDS in water by this method is 10 mg/L.Footnote 2020 High TDS concentrations can also be measured gravimetrically, although this method excludes volatile organics.Footnote 2121 The constituents of TDS can also be measured individually.
Total dissolved solids are not appreciably removed using conventional water treatment processes. In fact, the addition of chemicals during conventional water treatment generally increases the TDS concentration.Footnote 2222 Certain treatment processes, such as lime-soda ash softening and sodium exchange zeolite softening, may slightly decrease or increase the TDS concentration, respectively.Footnote 2323 Demineralization processes are required for significant TDS removal. Although the technology is available to reduce TDS levels significantly, the economic cost may be a major constraint.Footnote 2323 Reverse osmosis and electrodialysis would probably be the most economical processes for removing TDS from public water supplies.Footnote 2424
Health Considerations
Recent data on health effects associated with the ingestion of TDS in drinking water have not been identified; however, associations between various health effects and hardness, rather than TDS content, have been investigated in many studies. These data are discussed in the section on hardness. As well, some of the individual components of TDS can have effects on human health. Effects that can be attributed to specific constituents are discussed in separate reviews for those constituents.
In early studies, inverse relationships were reported between TDS concentrations in drinking water and the incidence of cancer,Footnote 2525 coronary heart disease,Footnote 2626 arteriosclerotic heart diseaseFootnote 2727 and cardiovascular disease.Footnote 2828,Footnote 2929 Total mortality rates were reported to be inversely correlated with TDS levels in drinking water.Footnote 2929,Footnote 3030
Conversely, a summary of an Australian study reported that mortality due to all categories of ischaemic heart disease and acute myocardial infarction was increased in a community with higher levels of soluble solids, calcium, magnesium, sulphate, chloride and fluoride, alkalinity, total hardness and pH, when compared with a community in which levels were lower.Footnote 3131 No attempts were made to relate mortality due to cardiovascular disease to other potential confounding factors. The results of a limited epidemiological study in the former Soviet Union indicated that the average number of "cases" of inflammation of the gall bladder and gallstones over a five-year period increased with the mean level of dry residue in the groundwater.Footnote 3232 It should be noted, however, that the number of "cases" varied greatly from year to year in one district, as did the concentration of dry residue in each district, and no attempt was made to take into account possible confounding factors.
Other Considerations
The presence of dissolved solids in water may affect its taste.Footnote 33-42 The palatability of drinking water has been rated, by panels of tasters, according to TDS level as follows: excellent, less than 300 mg/L; good, between 300 and 600 mg/L; fair, between 600 and 900 mg/L; poor, between 900 and 1200 mg/L; and unacceptable, greater than 1200 mg/L.Footnote 3737 Water with extremely low TDS concentrations may also be unacceptable because of its flat, insipid taste.
In addition to palatability, certain components of TDS such as chlorides, sulphates, magnesium, calcium and carbonates also affect corrosion or encrustation in water distribution systems.Footnote 2121 High TDS levels (above 500 mg/L) result in excessive scaling in water pipes, water heaters, boilers and household appliances such as tea kettles and steam irons.Footnote 4343 Such scaling can shorten the service life of these appliances.Footnote 4444
Rationale
- The most important aspect of TDS with respect to drinking water quality is its effect on taste. The palatability of drinking water with a TDS level less than 600 mg/L is generally considered to be good. Drinking water supplies with TDS levels greater than 1200 mg/L are unpalatable to most consumers.
- Concentrations of TDS above 500 mg/L result in excessive scaling in water pipes, water heaters, boilers and household appliances.
- An aesthetic objective of ≤500 mg/L should ensure palatability and prevent excessive scaling. However, it should be noted that at low levels TDS contributes to the palatability of drinking water.
References
Footnotes
- Footnote 1
-
Rainwater, F.H. and Thatcher, L.L. Methods for collection and analysis of water samples. Geological Survey Water-Supply Paper, U.S. Department of the Interior. U.S. Government Printing Office, Washington, DC (1960).
- Footnote 2
-
Garrison Investigative Board. Water quality report (Appendix A). Garrison Diversion Study, report to the International Joint Commission (1977).
- Footnote 3
-
Durfor, C.J. and Becker, E. Constituents and properties of water. In: Water quality in a stressed environment: readings in environmental hydrology. W.A. Pettyjohn (ed.). Burgess Publishing Company, Minneapolis, MN (1972).
- Footnote 4
-
Rawson, D.S. and Moore, J.E. The saline lakes of Saskatchewan. Can. J. Res., 22: 141 (1944).
- Footnote 5
-
Fisheries and Environment Canada. Surface water quality in Canada. An overview. Water Quality Branch, Inland Waters Directorate (1977).
- Footnote 6
-
Upper Lakes Reference Group. The waters of Lake Huron and Lake Superior. Vols. I to III, Parts A and B. Report to the International Joint Commission (1977).
- Footnote 7
-
Great Lakes Water Quality Board. Great Lakes water quality 1974. Appendix A. Water Quality Objectives Subcommittee report to the International Joint Commission (1975).
- Footnote 8
-
Beeton, A.M. Indices of Great Lakes eutrophication. Publ. No. 15, Great Lakes Research Division, University of Michigan, Ann Arbor, MI (1966).
- Footnote 9
-
Kormondy, E.J. Concepts of ecology. Prentice-Hall, Englewood Cliffs, NJ. p. 182 (1969).
- Footnote 10
-
Vaughn, J.C. and Reed, P.A. Quality status of southern Lake Michigan. J. Am. Water Works Assoc., 62: 103 (1972).
- Footnote 11
-
Dominie, K. Personal communication. Newfoundland and Labrador Department of Environment and Lands (1989).
- Footnote 12
-
Durocher, H. Personal communication. Ministère de l'Environnement, Gouvernement du Québec (1990).
- Footnote 13
-
Vajdic, A. Personal communication. Ontario Ministry of the Environment (1989).
- Footnote 14
-
Rocan, D. Personal communication. Manitoba Department of Environment (1989).
- Footnote 15
-
Nargang, D. Personal communication. Saskatchewan Department of the Environment and Resource Management (1989).
- Footnote 16
-
Spink, D. Personal communication. Alberta Ministry of Environmental Protection (1989).
- Footnote 17
-
Willoughby, B.A. Personal communication. B.C. Ministry of Health (1989).
- Footnote 18
-
Ontario Ministry of the Environment. Outlines of analytical methods. A guide to the occurrence, significance, sampling and analysis of chemical and microbial parameters in water. February (1975).
- Footnote 19
-
Singh, T. and Kalra, Y.P. Specific conductance method for in situ estimation of total dissolved solids. J. Am. Water Works Assoc., 67(2): 99 (1975).
- Footnote 20
-
Forbes, M. Personal communication. Canada Centre for Inland Waters, Burlington, Ontario (1988).
- Footnote 21
-
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).
- Footnote 22
-
Department of National Health and Welfare. Water treatment principles and applications: a manual for the production of drinking water. Canadian Water and Wastewater Association (1993).
- Footnote 23
-
Canadian Council of Resource and Environment Ministers. Total dissolved solids. In: Canadian water quality guidelines. Prepared by the Task Force on Water Quality Guidelines. Environment Canada, Ottawa, March (1987).
- Footnote 24
-
Clark, J.W., Viessman, W., Jr. and Hammer, M.J. Water supply and pollution control. 3rd edition. Harper & Row Publishers, New York, NY (1977).
- Footnote 25
-
Burton, A.C. and Cornhill, J.F. Correlation of cancer death rates with altitude and with the quality of water supply of the 100 largest cities in the United States. J. Toxicol. Environ. Health, 3(3): 465 (1977).
- 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).
- Footnote 27
-
Schroeder, H.A. Municipal drinking water and cardiovascular death rates. J. Am. Med. Assoc., 195: 125 (1966).
- Footnote 28
-
Sauer, H.I. Relationship between trace element content of drinking water and chronic disease. Univ. Ill. Bull., 71(108): 39 (1974).
- Footnote 29
-
Craun, G.F. and McCabe, L.J. Problems associated with metals in drinking water. J. Am. Water Works Assoc., 67: 593 (1975).
- Footnote 30
-
Crawford, M., Gardner, M.J. and Morris, J.N. Mortality and hardness of local water supplies. Lancet, i: 827 (1968).
- Footnote 31
-
Meyers, D. Mortality and water hardness. Lancet, i: 398 (1975).
- Footnote 32
-
Popov, V.V. Cholelithiasis and calculi, hardness of drinking water. Gig. Sanit., 33(6): 416 (1970).
- Footnote 33
-
Bruvold, W.H. and Pangborn, R.M. Rated acceptability of mineral taste in water. J. Appl. Psychol., 50(1): 22 (1966).
- Footnote 34
-
Bruvold, W.H., Ongerth, H.J. and Dillehay, R.C. Consumer attitudes toward mineral taste in domestic water. J. Am. Water Works Assoc., 59: 547 (1967).
- Footnote 35
-
Bruvold, W.H. Scales for rating the taste of water. J. Appl. Psychol., 52: 245 (1968).
- Footnote 36
-
Bruvold, W.H. Mineral taste and the potability of domestic water. Water Res., 4: 331 (1970).
- Footnote 37
-
Bruvold, W.H. and Ongerth, H.J. Taste quality of mineralized water. J. Am. Water Works Assoc., 61: 170 (1969).
- Footnote 38
-
Cox, G.J., Nathans, J.W. and Vonau, N. Subthreshold-to-taste thresholds of sodium, potassium, magnesium and calcium ions in water. J. Appl. Physiol., 8: 283 (1955).
- Footnote 39
-
Bryan, P.E., Kuzmunski, L.N., Sawyer, F.M. and Feng, T.H. Taste thresholds of halogens in water. J. Am. Water Works Assoc., 65: 363 (1973).
- Footnote 40
-
Pangborn, R.M. and Bertolero, L.L. Influence of temperature on taste intensity and degree of liking of drinking water. J. Am. Water Works Assoc., 64: 511 (1972).
- Footnote 41
-
Bruvold, W.H. and Pangborn, R.M. Rated acceptability of mineral taste in water. J. Appl. Psychol., 50: 22 (1966).
- Footnote 42
-
Pangborn, R.M., Trabue, I.M. and Little, A.C. Analysis of coffee, tea, artificially flavoured drinks prepared from mineralized waters. J. Food Sci., 36: 355 (1971).
- Footnote 43
-
Tihansky, D.P. Economic damages from residential use of mineralized water supply. Water Resour. Res., 10(2): 145 (1974).
- Footnote 44
-
McQuillan, R.G. and Spenst, P.G. The addition of chemicals to apartment water supplies. J. Am. Water Works Assoc., 68: 415 (1976).
