Residential water softeners are plumbed into the home’s water supply and work by eliminating dissolved minerals through a process called ion exchange. There are two basic types of water softeners: automatic (also known as self-regenerating) and exchange tank.  Both types have a mineral tank that is filled with small plastic beads (also known as resin) that are negatively charged. To balance the charge, positively charged sodium or potassium ions are present on the beads. Under normal use, hard water passes through the mineral tank. The calcium and magnesium ions in the hard water have a stronger positive charge than the sodium or potassium ions on the resin. Therefore, the calcium and magnesium ions replace the sodium or potassium ions on the resin. The water flowing through the softener is now considered “soft” because the majority of the calcium and magnesium in the water has been replaced with sodium or potassium.

Eventually, there will not be enough sodium or potassium left on the resin to effectively soften the water. Then the softener has to be regenerated. This is achieved by sending a brine solution containing highly concentrated sodium chloride (salt) or potassium chloride through the mineral tank.  The high levels of sodium or potassium in the brine force the calcium and magnesium off the resin, replacing it with sodium or potassium. The chloride present in the brine simply stays in solution. 

Automatic Water Softeners

Automatic water softeners have a separate brine tank that holds a salt or potassium chloride solution, which is used to regenerate the softener onsite. The softener is normally set to regenerate in the middle of the night, because soft water is unavailable during regeneration.  After regenerating the mineral tank, the brine solution is flushed to the sewer.  The chloride in the brine ends up at the wastewater treatment plant, increasing operating costs to remove chloride from the wastewater before it is released into the Santa Clara River.  New salt or potassium chloride must be added to the brine tank regularly to replace the salt or potassium chloride used to regenerate the mineral tank. Because chloride is not consumed during regeneration, all chloride sent to the mineral tank will be discharged to the sewer as spent brine.

Exchange Tank Softeners

Exchange tank softeners do not require the addition of salt or potassium chloride.  They work in a manner similar to automatic water softeners but feature a removable mineral tank that is replaced by a service provider with a fresh mineral tank when the sodium or potassium on the resin is depleted. The depleted tanks are regenerated by the service provider at off-site facilities permitted to discharge salty waste to sewers outside the Santa Clarita Valley.  These sewers convey wastewater to treatment plants that do not release water into the Santa Clara River and do not need to remove chloride during treatment. Therefore, exchange tank softeners do not impact operating costs for the wastewater system.