Primary contaminant concern is of a mineral nature

Q1 — How to address mineral contaminant reduction:

A1 — In general terms, concerns relative to mineral contaminants is referred to as a “hardness” problem. The most economically feasible technology for homeowners to address water hardness is by ion exchange, aka water conditioning — better known yet as water “softening.”

Typically, concerns about mineral contaminations are of a “cosmetic” nature rather than of a well-considered health-related concern. In fact, the typical hardness minerals (calcium and magnesium) could actually represent beneficial nutrients.

That said, I don’t mean to imply that cosmetic considerations are not important. Mineral contaminations in high levels of such things as iron can stain white porcelain rust-red, and high levels of calcium can build up calcified white deposits (scale) on chrome fixtures, and all of the high-in-concentration minerals can combine to “sclerose” water pipes, eventually leading to costly plumbing replacement jobs.

On the other hand, mineral concentrations in what is at least considered safe, potable water are typically not threatening to human health. Minerals such as iron and calcium are even taken as dietary supplements by some people. In short, common minerals in water may be problematic in a “cosmetic” sense, but they are seldom health-threatening.

Q2 — Don’t water softeners put salt into the treated water?

A2 — Yes, to some degree. The amount of sodium, usually measured in mg/l (milligrams per liter), in softened water is directly proportional to the overall hardness (usually expressed in grains per gallon) plus other mineral contaminants (i.e., iron) the softener is being asked to remove from the incoming water.

Remember, this technology is called “ion exchange.” In a nutshell, the exchange of ions in a water softener happens in a resin core of (usually) sulfonated polystyrene beads. These beads are saturated with sodium. As incoming water passes through the resin core, hardness minerals attach to the beads in exchange for a sodium ion, which is released into the flow of water.

You can calculate in very general terms how much sodium (salt) you would expect to be in your softened water by knowing the hardness + iron levels of the incoming water. According to the Water Quality Association (WQA), the ion exchange softening process adds sodium at the rate of about 8 mg/liter for each grain of hardness removed per gallon of water.

So, as example, if your incoming water has a total hardness value (hardness + iron) of 10 grains per gallon, the softener will add about 80 mg/liter sodium if all hardness minerals are removed. Additionally, in a National Inorganics and Radionuclides Survey conducted by EPA in the mid-1980s, about 3/4 of 989 water systems included had concentrations of sodium of less that 50 mg/l. So, the total sodium in that water, including what the softener would impart by ion exchanging for 10 grains per gallon, would be right around 130 mg/l sodium.

The FDA publication: “Scouting for Sodium and Other Nutrients Important to Blood Pressure” (FDA 95-2284) states that most American adults tend to eat between 4,000 and 6,000 mg of sodium per day, “…and therapeutic sodium restricted diets can range from below 1,000 mg to 3,000 mg per day.”

To try to put the amount of sodium in softened water in perspective, FDA 95-2284 lists the following nutrient guidelines for food labeling:

Low-sodium: 140 mg or less per serving (or, if the serving is 30 g or less or two tablespoons or less, 140 mg or less per 50 g of the food)

Very low-sodium: 35 mg or less per serving (or, if the serving is 30 g or less or two tablespoons or less, 35 mg or less per 50 g of the food)

Sodium-free: Less than 5 mg per serving

According to that scale, a “serving” can be interpreted to mean 50 grams in weight. Using established conversion tables and doing a little simple math, we can know that a 8-ounce glass of water will weigh about 240 grams — which would represent 4.8 servings (240 grams divided by 50 grams per serving). At 130 mg/l sodium for our example softened water, one 8-ounce glass of water would represent 31.2 mg sodium, divided by 4.8 (servings) = 6.5 mg of sodium per “serving” (just above what the FDA considers “Sodium-free”).

If a person with a properly functioning ion exchange water softener consumes the USA average of 2 gallons (256 ounces — or, 32 glasses) of water per day (USEPA published estimate in “Water on Tap” — which includes drinking, drink preparation (coffee, tea, juices) and cooking), and the hardness level is 10 grains per gallon, and that person’s incoming tap water is typical for the USA in averaging 50 mg/l of sodium or less — that person is getting about 998 mg of sodium per day attributable to the softened water. Note that the average American eats between 4,000 and 6,000 mg of sodium per day, so drinking softened water would represent between 15-20% of that person’s total daily intake of sodium.

Note: “fresh water” is defined as consisting of less than 1,000 mg/l of sodium (salinity). Sodium salinity (sodium chloride — NaCl) is usually included with other “salts” and reported in water analyses as TDS (Total Dissolved Solids).

Water with between 0 and 500 mg/L TDS is considered to be suitable for human consumption. Water containing up to 10,000 TDS can be treated to reduce TDS to drinkable quality levels. Waters containing in excess of 10,000 mg/L TDS are called brine, or simply salt water (sea water is approximately 20,000 mg/L TDS). [USEPA, Office of Ground Water and Drinking Water].

You would probably not taste the “salt” in water that contained 130 mg/l sodium. Note: the TDS test is useful as an indicator of general water quality, but should not be taken as an actual measurement of sodium levels. Typically, most of the TDS value will be represented by sodium salt, but other inorganic salts such as those of calcium, magnesium, potassium, bicarbonates, chlorides and sulfates will also conribute to the TDS analysis results.

It is also important to note that sodium is an essential nutrient. The Food and Nutrition Board of the National Research Council recommends that most healthy adults need to consume at least 500 mg/day, and that sodium intake should be limited to no more than 2400 mg/day. [Comparing that to the FDA’s estimate of 4,000 to 6,000 mg of sodium per day consumed, it looks like we Americans should back off the saltshaker a bit]

For those who need/want softened water, but would not want the additional sodium in their consumable water that a softener would impart, the best solution would probably be to follow the POE water softener with a POU (typically, under the sink) reverse osmosis (RO) drinking water system. NOTE: water filtration by GAC or KDF would not be the recommended technology for effectively reducing dissolved sodium salt. ESD offers an economical 30 gpd RO system for your consideration.

Q3 — What are the calculations to properly size a water softener?

A3 — Here’s how things work with water softeners. There are two tanks that come with the system. One tank is the actual ion exchange resin core tank. It is the one doing all the work to remove mineral contaminants as water passes through it. The other tank is a salt or brine tank. It only comes into play during the (if the unit is properly sized) once a week “regeneration” or “cleansing” cycle.

The idea behind properly sizing a water softener is to get one large enough — based on water analysis factors such as hardness, etc. and biased against the demand (number of people served) — so that it only needs to regenerate about once a week.

What regeneration does is to cleanse the resin core of the week’s worth of minerals it has removed from the flow-through water. This is done by “scouring” it with a brine solution. During the regeneration cycle, water is pumped to the salt tank to form a brine solution. That brine solution is then pumped back to the softener tank to clean the resin core by replacing all the grains of minerals with sodium ions on the resin beads. At the end of the regeneration cycle, the softener tank flushes the minerals-laden brine water down the drain and refills itself with fresh water.

Most homeowners set the regeneration cycle timer to have that occur at some odd hour when everyone is typically asleep and not using any water. If someone draws water during the regeneration cycle, they’ll get VERY salty water.

There are some who have a very low tolerance to sodium salt. For such individuals, the use of a water softener may be inadvisable. There are alternative “salts” that can be used to ion exchanging, such as potassium salt. That usually costs a bit more, but would offer an alternative to the more typical sodium (table) salt.

ESD offers a water softener sizing calculation worksheet here. It’s not rocket science, but it’s well worth the calculating to know that you are: a) not spending too much for an oversized water softener, or: b) not spending too little up front — but setting yourself up to spend more as you go in wasted water and salt by having to set the recharge cycle to happen more often than the reasonable once-a-week schedule.

NOTE: you will need reasonably accurate values for the the levels of iron and magnesium as well as the hardness rating on your incoming water. If you do not know these figures, it would be advisable to have a water analysis done on the incoming water. Water analyses aren’t free, but they’re probably worth the fee to know that you are properly sizing your water softener unit for your actual circumstances. ESD recommends as a trusted and fairly priced water analysis laboratory.

Q4 — What constitutes “hard” water?

A4 — Water hardness is classified by the U.S. Department of Interior and the Water Quality Association as follows:

Classification grains/gal
Soft 0 – 1
Slightly hard 1 – 3.5
Moderately hard 3.5 – 7.0
Hard 7.0 – 10.5
Very hard over 10.5