Onsite wastewater recycling (septic) systems
About a quarter of the 115 million homes in the U.S. today rely on onsite wastewater treatment systems, commonly called “septic systems.” And 40% of all new homes in the US utilize these systems which discharge household wastes into a controlled “septic field” in the soil which decomposes the waste anaerobically, absorbing nutrients into the soil and filters the water entering the environment. Because sodium can adversely affect the texture of fine clay soils and because salt is an effective bacteria killer, some have hypothesized that discharging an ion-exchange water softener into a septic system, the current practice in a quarter-million U.S. homes, would clog the soil filtering ability of the septic field and kill the beneficial bacteria which biologically degrade the wastes. Science has dispelled that mistaken notion.
Studies published as early as 1977 by the University of Wisconsin and by the National Sanitation Foundation exonerated salt in the failure of septic systems. More recent, rigorous controlled trials have reconfirmed that finding.
More “advanced treatment technologies” use aerobic digestion to process the wastes and these systems have proved difficult to maintain; many fail. While there is no evidence that salt discharges from water softeners is the cause of the failures, manufacturers of these units and the Water Quality Association, supported by the Salt Institute, is conducting further tests.