Under-Sink Water Filters and Hard Water: What Works in Australia

Hard water is a common issue in parts of Australia — particularly Perth and Adelaide. Here’s what under-sink filters can and can’t do about it.

See our full Under Sink Water Filters Guide or call us on 1800 789 781 for advice.

What Is Hard Water?

Hard water contains high concentrations of dissolved calcium and magnesium. It’s not a health risk — these are beneficial minerals — but it causes scale buildup in kettles, hot water systems, and appliances, and can leave spots on glassware and shower screens. Perth and Adelaide have notably hard water compared to Sydney and Melbourne.

What Under-Sink Filters Do (and Don’t Do) for Hard Water

Standard carbon under-sink filters do not soften hard water. They remove chlorine, sediment, and some heavy metals — but dissolved calcium and magnesium pass straight through a carbon filter.

Reverse osmosis systems do remove hardness minerals — the RO membrane blocks calcium and magnesium ions along with other dissolved solids. RO-filtered water is soft. However, RO also removes beneficial minerals, which is why many RO systems include a remineralisation stage to add minerals back at a balanced level. See our RO Guide.

Anti-scale cartridges (template-assisted crystallisation or polyphosphate) don’t remove hardness minerals but change their form so they don’t deposit as scale. These are useful for protecting appliances and plumbing in hard water areas. Browse our replacement cartridge range for anti-scale options.

The Best Solution for Hard Water in Australia

For drinking water in hard water areas: an RO system with remineralisation gives you soft, mineral-balanced filtered water from the kitchen tap. For protecting appliances and plumbing throughout the house: a whole house filter with an anti-scale stage. See our Whole House Water Filters Guide.

Frequently Asked Questions