Sodium in your Drinking Water

Salts and minerals naturally occur in nature and are leached into groundwater, or to waterways as water flows over rocks and substrate. The most common form of salt is sodium chloride (NaCl), better known as table salt, which usually occurs in a crystalline form. When sodium chloride is dissolved, the sodium ions and chloride ions are split and form independent complexes with water molecules. Consequently, both sodium and chloride are common, and may present problems as drinking water contaminants if they occur in high concentrations.

Sources of Sodium and Chloride

Sodium and chloride may enter the water stream by natural processes as mentioned above, or in areas situated close to the sea, these salts may be reach waterways by wind-blown sea spray. Sodium and chloride salts may also be introduced through human activities such as use of road salt to de-ice roads, storage and spills of road salt, discharges from water softeners, human and animal waste disposal, and leaching from landfill sites. Sodium is often an essential ingredient in many water treatment chemicals, thus trace levels of sodium can remain as drinking water contaminants.

Water softeners (ion exchangers) replace hard ions such as magnesium and calcium with a soft ion such as sodium or potassium. The sodium from the water softener may increase sodium levels in the drinking water it is treating, and the waste (containing dissolved salts) also adds to sodium levels in the waterbody that it is discharged into.

Health Effects of Salts in Drinking Water

Neither sodium or chloride salts are currently considered to pose any major health risk to humans as drinking water contaminants. The US Environmental Protection Agency (EPA) includes chloride on its list of secondary drinking water contaminants, meaning that it poses no direct health risk, but does cause secondary aesthetic problems to drinking water. The EPA recommends a maximum acceptable level of 250mg/L for chloride. Concentrations exceeding this may give water an unpleasant salty taste.

Sodium is neither listed as a primary or secondary drinking water contaminant, as levels are generally not considered to be high enough to warrant any threat to human health. However, while sodium is generally considered harmless to humans at low doses, sodium intake is associated with hypertension, and it may thus pose a health risk to individuals suffering from heart disease. Consequently, sodium is included on the EPA's Drinking Water Contaminant Candidate List (CCL), a list of drinking water contaminants that are currently not regulated, but may require attention in future. The EPA has currently set a guideline of 20mg/L as an acceptable limit for sodium for those individuals that are on a restricted sodium diet, but there is criticism that this may be far too low. However, the American Heart Foundation has recommended the same level for those that suffer from hypertension, as intake of sodium from food products is much higher than this, and generally poses more of a health risk than the trace amounts of sodium present in drinking water.

High concentrations of sodium and chloride ions have the potential to increase the conductivity of water, which can corrode water pipes and fittings. This can reduce the lifespan of plumbing fittings, and can also have health implications if toxic drinking water contaminants such as lead or copper are leached into household supplies.

Water Purification to Remove Salts from Drinking Water

Removing salts from drinking water is not a simple process, and unfortunately require more complex water purification technology that simple household water filters. There are two water purification methods suitable for removing dissolved salts such as sodium and chloride from drinking water: reverse osmosis, and distillation.

Reverse Osmosis is a water purification process whereby water is forced through a semi-permeable membrane at high pressure. The water is allowed to pass through the membrane, while dissolved salts and other minerals present in the water are retained behind the membrane.

Distillation is a method where water is effectively boiled, giving off steam, which when cooled and allowed to condense, produces drinking water in its purest form. During this water purification process, salts, minerals, and other impurities are separated from the water and remain in the boiling chamber.

References
New Hampshire Department of Environmental Services. Sodium and Chloride in Drinking Water. Environmental Fact Sheet: WD-DWGB-3-17. 2010.

US Environmental Protection Agency. “Sodium in Drinking Water.” Water Contaminant Candidate List. 19 Oct. 2011. web. 6 Dec. 2011.

http://water.epa.gov/scitech/drinkingwater/dws/ccl/sodium.cfm

 
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