2. Salinity: Facts and Figures
Over the years, a number of respected institutions have looked into the causes and effects of salinity. They provide us scientific data that inform policymaking and drive how we lead our lives.
The CASS study. Beginning in 2001, a consortium of researchers began a major study of the importation of TDS (salinity and other solids in water) into central Arizona. The Central Arizona Salinity Study (CASS) study consisted of two phases conducted over a four-year project term.
In its conclusions, the authors of the report acknowledge the negative effects of hard water. But the report also notes that the agricultural sector experiences economic losses as high TDS water reduces crop yields, requires additional fertilizers and soil additives, and additional water to flush salts below the root zone. As the authors summarize the problem:
Water with a high TDS concentration impacts virtually all sectors of society - residential, commercial, industrial, and agricultural. For the homeowner, salinity reduces the useful life of household appliances, such as water heaters, evaporative coolers, faucets, clothes washers and dishwashers. Homeowners also incur salinity “avoidance costs” such as buying bottled drinking water and installing water softening systems. The commercial sector (schools, hospitals, retail stores, etc.) encounters impacts similar to homeowners with water-intensive operations bearing higher costs. Some industries in central Arizona (such as food and beverage manufacturers and semiconductor manufacturing) require de-mineralized water, other industries require water softening. In such cases, relative costs are directly tied to the TDS content of the water they receive from systems.
The effect of salinity on crops has been well documented. Worldwide, millions of acres of land - in some cases dating back to ancient civilizations - have been rendered unproductive due to salt loading. The present day agricultural sector experiences economic losses as high TDS water reduces crop yields, requires additional fertilizers and soil additives, and results in a need to apply supplemental water to flush salts downward away from the root zone. Increasing salinity content of groundwater has left supplies in certain areas unusable for expanding urban growth without some form of treatment.
Among other key findings:
- Currently, over 1.75 million tons of dissolved salts are imported into central Arizona’s Maricopa, Pinal and Pima counties annually from the Salt, Verde and Colorado Rivers.
- Since about 1985, the Phoenix metropolitan area has been accumulating salts at a rate of about a million tons annually. This is equivalent to a pickup load of salt coming into the Valley every 15 seconds.
- Society adds salts into the water cycle through the use of fertilizers, water softeners, industrial water treatment, and many other activities.
- Because of society’s contribution, the total dissolved solids (TDS) concentration in wastewater is between 300 to 500 milligrams per liter (mg/L) greater than the TDS concentration of the potable water supply. The salts remain in the water as it passes through the wastewater treatment plant.
The study concluded: “Managing salinity is required for the long term sustainability of central Arizona. Over a million tons of salts are accumulating in the Phoenix Metropolitan area and salts are also accumulating, although at a less rapid rate, in … other places in central Arizona. Some groundwater has TDS concentrations which make it non-potable. As the population grows, there will be increasing pressure to use these impaired waters.”
HDR Study. In 2009, HDR Engineering, Inc and Arizona State University (ASU) teamed to conduct a study that focused primarily on the effectiveness of devices that claim to be alternatives to conventional water softeners. It was conducted at the behest of the Phoenix Water Services Department.
The authors of the study found that “TDS and its components have the potential to restrict the beneficial use of reclaimed water, increase water management costs, and decrease the economic and environmental sustainability of a region.” As in the CASS study, they also recognized the real problems associated with hardness, stating that the Phoenix area is known to have very hard water at 80-280 mg/L.
The study also examined some of the underlying causes of high salinity. According to the report:
- Source waters contribute about 42% of the total salts. Other salt sources include neighboring cities and residential, commercial and industrial activities that result in wastewater discharges.
- Based on previous studies, it is estimated that about 31% of homes in the city are using SRWS (self-regenerating water softeners). The level of TDS originating from SRWS is not consistent due to a range of salt and water efficiencies. The modeling results indicate that residential SRWS produce 4 to 22% of the total in each sewershed examined, while commercial SRWS produce 1 to 4% and industrial softening produces about 17%.
- The model estimates that 137,202 to 160,869 pounds of salt are added to Phoenix sewers from all water softening activities each day, about to 8 to 10% of the total salts being treated at the three wastewater plants.