Water softening systems remove the calcium and magnesium ions that cause hardness. The most widely used method is ion exchange, used in homes, residential blocks, hotels and industry. This page explains how it works and which parameters matter when you choose a system.
How Ion Exchange Works
- Service: hard water flows through a tank of resin beads. The beads hold sodium ions and exchange them for calcium and magnesium.
- Backwash: when the resin is saturated, water flows upward to loosen the bed and flush out particles.
- Brining: salt solution from the brine tank passes through the resin; sodium displaces the captured hardness.
- Rinse: excess brine is rinsed to drain.
- Refill: the brine tank is refilled with water to dissolve salt for the next cycle.
Key Components
| Component | What to look for |
|---|---|
| Resin | Food-grade, high-capacity cation resin; volume in litres |
| Pressure tank | FRP tank sized to resin volume (e.g. 10×35, 10×54, 14×65 inch) |
| Control valve | Runxin, Clack or similar; time or volume (metered) control |
| Brine tank | Separate or integrated in a cabinet |
| Bypass | Allows service without cutting the water supply |
Time-Controlled vs. Metered Valves
Time-controlled valves regenerate on a fixed schedule regardless of use. Metered (volume-controlled) valves count litres and regenerate only when the resin capacity is used, saving salt and water. For variable consumption, such as a holiday villa or office, metered valves are clearly better.
Single Tank, Twin Tank, Cabinet
- Cabinet: resin and brine tank in one body; ideal for apartments.
- Single tank: separate resin and brine tanks; villas and small blocks.
- Twin tank (duplex): uninterrupted soft water; hotels and commercial buildings.
Resin Capacity and Salt Use
As a rule of thumb, one litre of resin removes roughly 4–6 grams of hardness (as CaCO₃) per regeneration, depending on salt dose. Daily consumption × hardness tells you how many litres of resin you need for a sensible regeneration interval of several days. Undersized resin means frequent regenerations and high salt use.
Maintenance
- Use clean tablet softener salt; keep salt visible above the water.
- Check outlet hardness with a test kit.
- Service valve, injector and brine tank once a year.
- Protect resin with a sediment filter; remove iron before softening.
Compare softening with other technologies on limescale treatment systems and scale prevention vs. water softening. For prices see water softener prices.
Frequently Asked Questions
How long does softener resin last?
Typically 5–10 years, depending on water quality, chlorine and iron levels and maintenance.
Does a softener use a lot of water?
A metered softener uses only a small percentage of treated water for regeneration; time-controlled valves use more.
What salt should I use?
Clean tablet or pellet softener salt. Avoid rock or table salt, which can clog the brine tank and injector.