Posted May 7th, 2012

David M. Bauman, CWS-VI, CI, CCO, is technical editor of Water Technology®and a water treatment consultant in Manitowoc, WI. He writes a regular column called “Professor POU/POE,” that appears in each issue of Water Technology–both print and online versions. Water Technology is a leading trade journal read by water treatment professionals. It is online at www.watertechonline.com. The information below is adapted from a recent article.

The “Professor” here address a frequently voiced concern about the amount of sodium that water softeners add to drinking water.

First keep in mind that there is already sodium in the untreated water. This cannot be avoided, so potential softener owners will have sodium in their water with or without softening.

Then the question is how much sodium will be added by softening the water. Frequently, the sodium added is much less than that which is in the raw water.

My favorite way to respond to this is to calculate the amount of sodium added by softening then compare it to the existing sodium and/or to the sodium in some common foods or beverages.

Since hardness is exchanged for sodium, start with the amount of hardness, and then convert it to the equivalent amount of sodium:

• GPG (grains per gallon) total hardness as CaCO3 (calcium carbonate … total hardness is always expressed as its calcium carbonate equivalent) is exchanged for an equal value of sodium as CaCO3. So, if the hardness is 20 gpg as CaCO3, the sodium added is 20 gpg as CaCO3.

• Then, multiply gpg Na (sodium) as CaCO3 x .460 (to convert Na as CaCO3 to Na as Na). 20 gpg Na as CaCO33 becomes 20 x 0.460 or 9.2 gpg Na as Na.

• To compare with the common way of expressing sodium, convert Na in gpg to Na in mg/L (milligrams per liter, same as ppm). Multiply 20 gpg Na times 17.1 to determine that there will be 157 mg/L (ppm) Na added during softening.

• To phrase this as a common volume of water multiply 157 x 0.24 to get 38 mg of sodium in 8 oz. of treated water.

• The above steps were given for educational purposes. A short-cut would be to multiply the total hardness of 20 gpg x 1.89 to get the same 38 mg per 8 oz. glass of softened water.

To compare this to common sodium levels in foods and beverages, I refer to the WQA technical paper titled “Sources of sodium in the diet.” This reveals that a slice of white bread contains 161 mg, a tablespoon of ketchup contains 204 mg and a can of Pepsi-Cola contains 38-49 mg of sodium. Given these levels, the amount of sodium added by softening seems quite inconsequential.

Here are a couple of items from Pure Water Gazette numerical wizard B. Bea Sharper to elaborate the relative significance of this added sodium:

Amount of sodium added to an 8 oz. glass of water by a water softener processing 7 grain hard water– 13 mg.

Amount of sodium in an 8 oz. glass of 7 grain hard water after it has been processed through a water softener then an undersink reverse osmosis unit– 0.6 mg.

Amount of sodium in a slice of white bread– 161 mg.

Footnote from the Occasional: I don’t want to muddy the softened waters, but you should note that there is some slight of hand taking place, The 1.89 times grains per gallon of hardness is yielding not mg per liter, the usual measurement of water constituents, but mg per 8 oz., a common water serving size. Therefore, the softener isn’t adding 1.89 mg of sodium for each grain of hardness it removes, but about four times that amount. A better multiplier would be 7.5 mg/L sodium added for each grain of hardness removed.

Here’s a clip from a nutrition website on the same subject:

For most individuals, the amount of sodium present in softened water is not a health problem. If however, you are trying to maintain a low sodium diet, this can add to your difficulties.

The amount of sodium in softened water can vary. According to a paper by Yarows et al., (Sodium concentration from water softeners, Arch Intern Med. 1997 Jan 27;157(2):218-22) the sodium concentration of softened well water averaged 278 mg/L but the variation was very large. Levels from 46 to 1219 mg/L were observed. 17% of households had sodium levels above 400 mg/L. The amount of sodium that gets added depends on how hard the water is to start with. If the water is very hard then the sodium level will be higher, as shown in the table below.