The most compelling arguments for softening hard water are economic: the high cost of replacing plumbing infrastructure, fixtures, faucets, water heaters and electrical appliances damaged by "lime scale." Scale accumulations may also cause losses in appliance efficiency and dramatic increases in electricity consumption. As water is heated, hardness minerals come out of solution and precipitate as scale. Water heaters, dishwashers and glass shower doors are the most common sites of scale accumulation. Extreme hard water can also be annoying for bathing and laundry.

Passing water through an ion-exchange resin tank is the most common method of hardness reduction.

Positively charged ions (cations) are exchanged for like-charged sodium or potassium ions attached to the resin. When the resin is no longer effective (estimated by the removal capacity of the water and the number of gallons used), it is regenerated on demand (not on the basis of a preset time interval regardless of water usage) using a brine solution that is discharged to a drain line, a leachfield (French drain), or septic tank. Pretreatment to remove contaminants that interfere with ion exchange, particularly iron and sediment, is commonly required for well water.

Softening is controversial both because of the water used in backwashing and chloride discharge. There is also controversy as to whether waste brine is injurious to leachfields and septic tanks. The New Mexico Environment Department's liquid-waste program is increasingly concerned with any potential water contaminants entering septic tanks.

Ion-exchange technology will continue to evolve with improved efficiency, but the technically similar anion exchange process (contaminant-specific resins using negatively-charged ions) will remain the most practical method for removing contaminants of the greatest health concerns (arsenic, nitrates and radionuclides) in the Santa Fe area.

The biggest future paradigm shifts in water treatment will involve salt-free systems, new filtration methods, and turnkey treatment and disposal of contaminants with the highest-known risks to human health. Alternatives to conventional ion exchange, such as magnets and catalytic systems, do exist; but the buyer should be wary as these systems also have limitations and most are unproven. The fact that many of these "salt-free" systems require backwashing is often cleverly omitted.

In the arid Southwest, environmentally responsible water-treatment companies offer tested alternatives to ion exchange. One of the most promising developments involves nanotechnology, wherein specialized resins create atomic-level nucleation sites (seed crystals) by template-assisted crystallization. Calcium and magnesium ions accumulate at crystallization sites on the resin, slough off and pass through the water system in colloidal suspension. No salt, chemicals or electricity are required. Because the system does not require backwashing water, no drain is required. However, as with any other method of water conditioning, this technology can only be successful if the water chemistry is determined suitable for its application.

Stephen Wiman has a background in earth science (Ph.D. in geology) and is the owner of Good Water Company in Santa Fe. He may be reached at 505-471-9036 and skwiman@goodwatercompany.com.

Originally published 9/2/2007 in Santa Fe New Mexican's Real Estate Guide p124