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The Chemistry Involved in ‘Softening’

A typical water softener softens water by ion exchange, which involves the exchange of the hardness minerals (chiefly calcium and magnesium) for sodium or potassium minerals. The exchange takes place by passing water containing hardness minerals over ion exchange resins in a tank. As the calcium and magnesium contact the resin in their travel through the tank, they displace sodium or potassium ions. The displaced sodium or potassium ions pass downward through the resin “bed” and out the softener drain; thus, the softener delivers “soft” water (Paso Robles 2003). Therefore, a softener merely exchanges one group of non-toxic elements for another group of non-toxic elements (Metropolitan 2001).

What the Chemical Changes Entail

Salt brine persists in the softened water to the point of use. A typical wastewater treatment facility removes very little of these mineral concentrations from the waste stream and so they are passed on to the environment.

Sodium really has no redeeming value in the environment outside of saltwater or brackish water ecosystems. It has been declared as the biggest contaminate affecting water supplies in the nation and the world. Water with salinity levels above 1,000 mg/l is of questionable use for irrigation and industrial customers.

As salinity increases, laundry detergents work less efficiently, plumbing fixtures and home appliances wear out faster and industry incurs higher treatment costs for boilers, cooling towers and manufacturing processes, and farmers experience reduced crop yields (Paso Robles 2003).

The Pros and Cons of Treatment

Water softeners reduce the “hardness” of the water, which can have several benefits for consumers: smaller amounts of soap and detergents (non-synthetic) are necessary for cleaning processes; reduced staining, spotting, scaling; and energy saving in water heating due to less scaling (Paso Robles 2003).

Cons: One of the disadvantages of soft water is that it is neither healthy nor desirable for drinking. Since water is a universal solvent, most materials, especially metals, are partially soluble in water. Therefore, if water is heated or softened it becomes much more aggressive at leaching metals from water lines. Lead in soldered joints and copper in pipes and faucets are particularly vulnerable, and these are two of the heavy metals that shouldn't be present in significant amounts in your drinking water.

Soft water is also aggressive at leaching metals (like lead) from your faucets. This means that if you have soft water, there is a great chance that your initial drawing of cold water will have a higher lead content than normal. Hot or warm softened water from the tap should never be used for cooking or drinking water as it could be higher in heavy metals.

The zeolite beads from water softening systems may back-siphon into your toilet tanks, and the soft water may attack vital plumbing parts.

A water softener can increase your sodium intake.

A softener can be costly to run since they can waste up to 120 gallons for every 1,000 delivered.

A water softener is not designed (nor is it effective) to remove lead and other metals, chlorine, taste/odor compounds nor chlorine by-products (Metropolitan 2001).

The discharge of salt brines from the regeneration of water softeners into the wastewater collection system has a negative impact on recycled water and wastewater effluent. Higher salinity increases the treatment costs and reduces the potential for reuse of wastewater for non-potable irrigation and industrial purposes. It can also impairs a wastewater treatment agency’s ability to comply with discharge standards for total dissolved solids (TDS) which is a measure of the total concentration of dissolved minerals in water (Paso Robles 2003).

Metropolitan Government of Nashville and Davidson County. 2001. “Soft Water, It’s Not For Drinking.” http://nashville.gov/water/soft_h2o.htm. Accessed 20 January 2003.

Paso Robles City Wastewater Treatment Division. 2003. “Water Softeners Issues.” http://www.prcity.com/government/departments/publicworks/wastewater/water-softeners.asp. Accessed 20 January 2003