I've recently moved to the country, and my new water supply comes from a well which is equipped with a greensand filter and a water softener. Having never used a softener before, I was concerned about the quality of such treated water. The local health department told me that softening increases the sodium content of the liquid and — given the emphasis now placed on low-salt diets — I wondered whether I should have my drinking supply bypass the softener.
Likely yes, but only after you understand the situation better and have found the answers to some questions peculiar to your location and circumstance. There is, you see, no universal answer.
Ground water from wells often contains naturally occurring minerals dissolved in low to medium concentrations. Depending upon the geology of your area and the depth of your well, your water may contain fair concentrations of such dissolved ions as calcium, magnesium, iron, manganese, and a host of other metals. In some circumstances, the concentrations of particular ions can be so high that there are excellent medical reasons either to remove them or to find an alternative source of drinking water. In most situations, though, the dissolved minerals impart properties that folks find make the liquid undesirable only for certain uses. For example, calcium and magnesium make water “hard”, thereby interfering with the lathering and cleansing ability of soap . . . while iron and manganese may give water an objectionable taste, odor, or color.
Most water softeners operate by exchanging sodium ions for other metal ions (this takes place as the water passes through the tank containing the so-called ion exchange resins). The water is softened by the removal of the ions responsible for “hardness” or “off” color and taste, and the introduction of sodium ions in their place. (Be careful here, though: There art many other natural and synthetic substances that may cause taste and/or odor problems, so don't assume that such irregularities will disappear upon the installation of a softener.)
Before making a decision about your drinking supply, however, you need to further analyze your particular setting. You must rind out the mineral composition of the well water before it's treated, so you can determine the nature of your problem and estimate (perhaps with the help of a local chemist) what the sodium concentration would be after softening. Then if the softened water does contain, say, more than 20 part per million (PPM) of sodium, you need to determine whether you can bypass the softener without causing a taste and/or odor problem.
— David Burmaster, a consultant on surface- and ground-water quality and hazardous waste management.