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Sources of total dissolved solids in drinking water
Total dissolved solids (TDS) is a measurement of the amount of dissolved ions in water. It is predominantly comprised of inorganic salts (calcium, magnesium, potassium, sodium, bicarbonates, chlorides and sulfates), many of which are necessary life-sustaining nutrients. But the measurement may also contain lesser amounts of dissolved organic matter. Water can easily pick up impurities from natural and man-made
sources because it is such an efficient solvent. Natural sources of TDS in drinking water include mineral springs, carbonate deposits, salt deposits, and sea water intrusion. Other sources can include sewage, urban and agricultural run-off, industrial wastewater, chemicals used in the water treatment process, the piping or hardware used to distribute the water, salts used for road de-icing, anti-skid materials, and more.
The indicator test for this drinking water contaminant is done to determine the general quality of the water. The TDS test only provides a qualitative measure of the amount of dissolved ions, but it does not provide information about specific dissolved ions. Other indicators of high TDS are hardness, scale formation, bitter taste in drinking water caused by calcium carbonate (CaCO3) and magnesium carbonate (MGCO3), and salty or brackish taste resulting from sodium chloride (NaCl) and potassium chloride (KCl). The latter can increase the corrosive ability of water. High TDS levels are also responsible for leaving water spots on dishes and white mineral buildup on water faucets and swamp coolers. It can also affect the efficiency of hot water heaters.
Potential health effects of total dissolved solids (TDS) in drinking water
As mentioned above, the TDS test is an indicator of aesthetics. An elevated level of TDS, by itself, does not indicate that the water presents a health risk. However, elevated levels of specific ions included in the TDS measurement, such as nitrate, arsenic, aluminum, copper, or lead, could present health risks. If an indicator test shows elevated TDS, specific analysis is then required for each contaminant to determine potential health effects.
Testing for total dissolved solids (TDS) in drinking water
The quality of water supplied by public water systems is regulated by the U.S. Environmental Protection Agency (EPA). EPA tests are divided into two categories — Primary and Secondary Maximum Contaminant Level Standards. TDS is classified under the secondary standards, which are based on aesthetic factors such as color and staining properties of water rather than potentially harmful health effects.
The standard in drinking water for TDS is 500 milligrams per liter (mg/l). Secondary standards are guidelines and are not enforced; however, an elevated TDS may mean that the water source contains elevated levels of nitrate and other contaminants that are regulated and enforced under EPA’s Primary Maximum Contaminant standards.
Approximately 15 percent of Americans rely on private drinking water supplies. These supplies are not subject to EPA standards, although some state and local governments do set rules to protect users of these wells. The determination of water quality in private wells is the responsibility of the homeowner. Consumers wanting to know the concentration of TDS in a private water supply will need to have the water tested. Local Cooperative Extension offices can provide a list of laboratories.
Here are some steps you can take to help protect your private well:
- Have your water tested periodically. It is recommended that water be tested every year for total coliform bacteria, nitrates, total dissolved solids, and pH levels. If you suspect other contaminants, test for those as well.
- Since these tests can be expensive, spend some time identifying potential problems before choosing specific tests.
- Always use a state certified laboratory that conducts drinking water tests.
- Testing more than once a year may be warranted in special situations:
- Someone in your household is pregnant or nursing;
- There are unexplained illnesses in the family;
- Your neighbors find a dangerous contaminant in their water;
- You note a change in water taste, odor, color or clarity;
- There is a spill of chemicals or fuels into or near your well;
- When you replace or repair any part of your well system.
Options for total dissolved solids in drinking water
The best option for dealing with elevated TDS depends on the specific ions present and their concentration. For example, if the elevated TDS is due to calcium and magnesium, a water softener is a good option. The process may not reduce the TDS concentration, but it will manage the aesthetic problems associated with the ions. If the problem is associated with an elevated concentration of nitrate, a reverse osmosis system or distillation unit can be used. The best option for dealing with TDS in drinking water should only be determined after analysis of the specific ions contributing to the TDS measurement.
Resources
“Well: Arizona Owner’s Help. 2009. Retrieved from http://wellownerhelp.org/fact-guide.html. July 6, 2010.
References
Hassinger, E., Doerge, T., Baker, P. 1994. Water Facts: Number 1. Test your well for safety. Retrieved from http://ag.arizona.edu/pubs/water/az9414.pdf. July 6,2010.