Two layers in one tank
The tank is fiberglass, ten inches across and fifty four tall, and it holds a cubic foot and a half of media in three layers. On top is coconut shell carbon. Chlorine and chloramine stick to its surface as the water passes, and the pool smell and taste go with them. Carbon does not grab minerals or metals, and it is not meant to.
Below the carbon is the softening resin, ten percent crosslinked and made in Camden, New Jersey. Each bead holds sodium. Calcium and magnesium, which are what make water hard, stick to a bead harder than sodium does, so the water gives up its hardness and takes a little sodium in exchange. Nothing is filtered out in that trade. One dissolved thing is swapped for another, and the top of the bed fills up first. Gravel at the base supports the bed, the water collects there, comes up the center tube and leaves the valve for every tap, shower and appliance in the house.
The valve decides when
The resin is a sponge that fills up. Once the beads are full the water goes through hard, so the valve on top has one job: know when that is about to happen. A timer valve guesses. It regenerates every so many days, set once at install, and has no idea how much water you used. Two weeks away and it still runs twice on clean beads. A week of guests and it runs out early and passes hard water until its day comes.
Our valve is metered. A small meter in the head counts every gallon, the plumber types in your hardness at install, and the valve knows how many grains the beads have taken on. When use crosses into the reserve, about a day of capacity, it marks tonight as the night and waits until two in the morning, so nobody is in the shower. The demand picks the day and the clock picks the hour. It also keeps a 72 hour memory, so a power cut does not lose the count or the hour.
Regeneration, step by step
- Backwash. The valve reverses the flow. Water goes down the center tube and up through the bed, lifting it, loosening it, and carrying any grit out to the drain.
- Brine draw. The valve draws salt water from the brine tank, about nine pounds of salt dissolved in it, and pushes it up through the resin from the bottom. The strong sodium knocks the calcium and magnesium off the beads and carries them to the drain. Upflow puts the freshest brine on the beads the house water touches last, which uses less salt for the same result.
- Rinse. Fresh water pushes the last of the brine out to the drain.
- Refill. A measured amount of water goes back into the brine tank, where it sits on the salt and dissolves what it needs for next time.
By morning the counter is at zero and the beads are loaded with sodium again. The salt pellets are the only thing you ever touch: a 40 pound bag every month or two, kept about half full in the brine tank.
Why the reverse osmosis is at the kitchen tap
The whole house system treats the water you live in: hardness and chlorine, what you feel on your skin and see on your fixtures. It does not touch what is dissolved and invisible. Lead from old solder, nitrate, arsenic, fluoride, the forever chemicals, and the little sodium the softener added are all still in the water, and for a shower or a water heater that is the right water.
The reverse osmosis at the kitchen sink is a different mechanism. Pressure pushes water against a membrane with openings around 0.0001 micron. Water molecules fit through and almost nothing dissolved does, ninety four to ninety nine percent of dissolved solids rejected and sent to the drain. The last stage puts a little calcium and magnesium back so it tastes like water and sits at a neutral pH, and it runs to its own faucet through plastic tubing. The membrane is slow and thirsty, about fifty gallons a day against the twenty seven a minute the house system flows, so it treats the water you drink and cook with and leaves the rest of the house to the softener and the carbon.