A limescale filter is a cartridge-based device that reduces the effect of hard water on a specific appliance or a whole home inlet. It is the most economical first step against limescale, especially where a full water softener is not possible.
Types of Limescale Filter
Polyphosphate (Siliphos) cartridges
Siliphos crystals dissolve slowly and keep calcium from sticking to hot surfaces. Ideal in front of a combi boiler, washing machine or dishwasher. No power or salt; replace every 6–12 months.
Resin cartridges
10″ cartridges filled with cation resin remove hardness for a limited volume of water, then must be replaced. Useful in low-consumption homes or as an extra stage in a filter set.
Multi-stage filter sets
Sets such as our Atlas and Green Aqua triple systems combine sediment, carbon and a scale stage (Siliphos or resin) on one bracket for the home inlet. They reduce sand, odour and scale effects at low cost. See well water treatment systems for all sets.
Which One for Which Need?
| Need | Suitable filter |
|---|---|
| Protect one boiler or washing machine | Polyphosphate cartridge |
| Home inlet, moderate hardness, sediment | Triple set: sediment + carbon + Siliphos |
| Small home, no drain for a softener | Set with resin cartridges |
| Whole house, hard water | Cabinet water softener |
When to Replace the Cartridges
- Siliphos: when the crystals are mostly dissolved, usually 6–12 months.
- Sediment: when it turns dark or pressure drops, 3–6 months.
- Carbon: every 6–12 months or when taste/odour returns.
- Resin cartridges: when outlet hardness rises (check with a test kit).
Installation
10″ filter sets mount on a wall bracket at the inlet with 3/4″ or 1″ connections. Fit a valve before and after so cartridges can be changed without draining the system. Big Blue 20″ housings are used for higher flow.
Price
Filter sets are the lowest-cost limescale solution, from about $40. Compare with softeners on water softener prices and read scale prevention vs. water softening.
Frequently Asked Questions
Does a limescale filter soften water?
Polyphosphate filters do not. Resin cartridges soften a limited volume. For real whole-house softening, use a water softener.
Is polyphosphate safe in drinking water?
Food-grade polyphosphate is used in drinking water treatment at low doses. Follow the manufacturer’s instructions.