Resolving the issues
Water softeners are one form of ion exchange devices used for the improvement of water quality. They are very useful in removing iron and other heavy metals from well water. However, their most common use is in the removal of the “hardness” ions, calcium and magnesium that cause scale buildup in plumbing, staining of fixtures and the spotting of glassware in dishwashers. Soap and shampoo does not lather well in hard water and results in rougher skin and hair after showering. Hot water appliances experience a heavy buildup of deposits that reduces their effectiveness and shortens their lifespan and softeners largely eliminate those problems.
Unfortunately, the great advantages produced by softeners may be accompanied by certain problem issues. After a water softener completes its cycle, the hardness minerals removed from the water have to be purged off of the ion exchange resin in order for it to be ready for its next cycle of operation. This is done by “exchanging” them for sodium. During this backflushing procedure a small amount of sodium chloride is released into the environment where some claim it may have a negative impact. Because of this, some communities have severely regulated or even banned their use.
Considered in isolation, chloride discharges may be perceived to have a negative environmental impact, however, in the case of water softeners, there are a number of other factors that have to be considered.
A study was recently conducted by scientists at New Mexico State University to measure and quantify differences, if any, in energy consumption of household water heaters installed and operated on hard versus softened water supplies.
The NMSU study was performed in the laboratory on 16 water heaters - four new heaters and 12 heaters removed from actual households in the Las Cruses, New Mexico area. Used heaters were selected to obtain a broad range of in-service time from 5 - 15 years and varying amounts of sediment-scale deposit. The test groups were chosen so that half of each group had been operated exclusively on the area's untreated hard water (average water hardness ranged from 9.4 to 14.3 grains per gallon), and the other half of each group had been operated exclusively on water from the same source but which was first softened by home water softeners to remove hardness minerals. The energy consumed by each water heater was monitored at the NMSU labs for 14 days under typical residential hot water usage patterns.
In terms of additional energy consumed, the group of used gas water heaters took 29.57% more BTU's than the group on softened water to proved the same amount of hot water. The used electric water heaters took 21.68% more BTU's.
Hard water contributes to the buildup of a layer of insulation in the form of scale between the water and the heat source. Scale is a poor conductor of heat. In order to heat the water it is first necessary to heat the scale that has built up in the tank. The energy used in heating this scale is largely wasted and these units work harder and use more energy to deliver a given amount of hot water than heaters which do not have the handicap of hard water scale.
The researchers removed and weighed the scale that had accumulated in the used heaters and found 3.86 lbs in a six year old gas heater to almost 40 lbs in a ten year old unit. The amount removed from the electric heaters varied from 15 to 39 lbs.
An executive summary of this research can be found here (pdf 724.50 kB) .
Soaps and detergents
It has long been known that far less soap or detergent is needed when washing with soft water. Studies have demonstrated that the requirement for soap and detergent can double in hard water. Modern detergent formulations have been adapted to take hard water into account through the use of additives such as phosphates, but there continues to be considerably different usage rates between hard and soft water. Both the additional detergent needed and the added ‘softening’ agents significantly increase the environmental burden of laundry and washing activities. Therefore, the possible environmental effects of sodium chlorides in water softener discharges must be balanced against the significant benefits derived from the reduced use of soap and detergents.
An excellent history on the environmental problems associated with phosphate based detergents was prepared by the University of Colorado .
Impact of water hardness on chloride toxicity
Recent research vigorously supports the concept that increased water hardness can reduce chloride toxicity. Thus far, the research has been exclusively observational, that is, the effect is observed but there is no explanation yet as to why it happens. This is an exciting new development in the field of environmental science. With reference to water softening activities, this phenomenon has tremendous significance because water softening is normally employed where hard water exists. That being the case, the environmental impact of softener discharges released into the local hard water source is likely to be far less than originally perceived.
A recent study conducted in Iowa reflects the impact of hardness on chloride toxicity and we expect to see many more similar studies in future. As the research is published, it will be posted here.