TIL: Water Softeners

We wake up to hear an odd sound carried through the forced-air ducts. Furnace is loud, I think. My wife precedes me downstairs and, finding the sound louder, heads to the basement.

“Water in the basement!” comes her yell. I bound down the stairs two at a time and start shutting off water valves to stem the flow of a 3/4″ coldwater supply emptying through the water softener and onto the floor.

Water softeners are a piece of almost necessary equipment in the part of Canada where I live. Hard water is water that contains dissolved minerals (usually Calcium and Manganese) that, when present in sufficient amounts, can form “hard water scale.” This usually shows up on heating surfaces (the inside of kettles and water heaters) and on drying dishes (in the form of cloudy spots). Hard water’s not toxic or anything, but it’s a pain, and our water’s well into the category the USGS calls “very hard.” So we soften it.

Conventional water softeners work by exchanging those dissolved mineral ions (mostly Calcium around here) for salt ions (Sodium or Potassium) in tiny little resin beads kept in a column called the “resin tank” (or “mineral tank”) which you hook up to your water supply. The beads are made up of a compound to which salt binds less strongly than other ions (because it prefers ions missing two valence electrons, if you remember your High School Chemistry). Thus, when a bead with a bound salt is presented with a free-floating Calcium ion, the bead ditches the salt into the water and snatches up the Calcium.

The resulting water does not taste salty and does not meaningfully contribute to dietary salt intake, in case you were wondering.

Eventually these beads become full of these mineral ions. To return them to previous performance levels, they are soaked and flushed with a salt brine. Due to the brine’s high concentration of salt ions, the hardness ions leave the resins to form an equilibrium between the beads and the brine. Then the waste brine (now full of hardness ions as well as quite a lot of the salt) is sent down the drain.

To generate the brine, water is pumped into a salt storage tank (or “brine tank”) and then is left to dissolve salt. This salt is the only consumed quantity in this process, and must be regularly topped up (usually by purchasing 24kg bags of softener salt pellets at local grocery stores for under $6 a bag).

The whole recharge process takes about two hours.

Water softeners have an operating lifetime similar to that of the plumbing fittings you need to install it: ten to fifteen years.

Near as I can figure it, the water softener that decided to flood my basement was 14 years old when its resin tank decided to rupture catastrophically during a 2am recharge cycle. Two hours later, recharge cycle complete, it flipped the valve back to supply the house with soft water and then supplied itself with all of the house’s water.

Luckily my floor drain was nearby and could handle the water flow, so the only “damage” was a little splashed carpet in the next room and some garbage I’d been meaning to throw out. I’m not looking forward to the water bill next month, but I’m happy my furnace is installed on feet for just this sort of occasion.

I did get a nice close-up view of those tiny ion-exchange resin beads, though, as they had been spread all over the basement floor. They look like transparent cornmeal. When wet they kinda have the consistency of mashed potatoes.

One on-sale water softener from Canadian Tire and one plumber’s visit later, I’m once again living in the land of soft water. For the next ten to fifteen years.

So now I know rather more than I previously did about water softening. And so do you.