Difference Between Water Softener & Water Filter

Water softeners and filters are designed to remove different kinds of contaminants.

Water filters remove contaminants from water to help make it safer for drinking. Water softeners, by contrast, remove calcium and magnesium ions from water. These ions can combine with soap and other substances to form deposits and scale, so while they are not harmful, they are often a nuisance. Both water filters and softeners remove dissolved substances from the water, but softeners specifically remove hard water ions to make the water "softer."

Water Softeners

A typical water softener has a mineral tank filled with small resin beads; negatively charged sites on these beads attract and trap positively charged ions. Initially, these negatively charged sites are occupied by sodium or potassium ions, but the sodium/potassium ions are only weakly bound, so they are displaced by magnesium and calcium ions in the drinking water as it flows through. Once the sites on the beads are all occupied by calcium or magnesium ions, the mineral tank must be regenerated by flushing it with brine; the high excess of sodium ions in the brine water will displace the calcium and magnesium ions so they can be washed away.

Filters

A filter removes contaminants from the water. There are many different kinds of filters, each of which has advantages for certain applications. Activated carbon filters, for example, contain positively charged absorbent carbon in the filter, which acts to trap various contaminants like bad tastes and odors. Distillation units boil the water and then recondense it to eliminate heavy metal contaminants. Reverse osmosis units eliminate most kinds of contaminants using semi-permeable membranes that permit only water to pass through, while UV disinfection systems kill microorganisms in the water.

Comparison

A water softener is essentially a type of filter, since it removes calcium and magnesium ions from the water. It does not and will not, however, remove other contaminants like microorganisms. Filters like activated carbon systems, by contrast, do not remove calcium and magnesium ions and thus cannot soften the water. Some filtration options like reverse osmosis can reduce hardness, although an ion exchange water softener is designed specifically to treat excessively hard water.

Benefits

Which choice is most appropriate --- a water softener or another filtration system -- depends on what kinds of contaminants are present in your water supply. If water hardness is your only issue, a water softener will probably be most appropriate, although it's important to note that water softeners do increase the water's sodium content. Water softener prices range from $300 to $1,000 or so. A reverse osmosis or distillation system can help reduce water hardness but is typically a less efficient approach for this problem, so it should not be your first choice for hard water. Costs for RO systems range from $200 to $500 plus installation, and maintenance usually runs $50 to $120 a year. Distillation removes all contaminants but is very energy-intensive; a home-scale distillation system usually costs from $450 to $1,450, and its operation can add substantially to your electric bill. Activated carbon and UV systems will deal with certain other kinds of contaminants but do not affect water hardness.

References

• University of Wisconsin Stevens-Point: Water Softener Use Raises Questions for Septic System Owners
• Lenntech: Water Purification Steps FAQ
• NRDC: Consumer Guide to Water Filters
• Arizona State University: Water Treatment Options