For most households, the best starting point is an under-sink reverse osmosis (RO) system with independent evidence that the exact model reduces arsenic under conditions matching your water. Test the source water first: arsenic III, or As(III), is harder to remove than arsenic V, or As(V), and may require oxidation or specialised treatment.
Until treated-water testing confirms an acceptable result, use a safe alternative supply for drinking, cooking and food preparation. Boiling does not remove arsenic and may concentrate it as water evaporates.
Why under-sink RO is usually the best default
An arsenic-verified under-sink RO system treats water at a dedicated kitchen tap, making it practical when only drinking and cooking water require treatment. The membrane provides the main arsenic reduction; sediment and carbon prefilters mainly protect the membrane. Ordinary carbon jugs and cartridges should not be relied on unless the complete product has independent evidence for arsenic reduction.
Check the public certification listing or test report for the exact model, not just a general certification logo or “heavy metals” claim. For RO systems, an arsenic reduction claim may be certified under NSF/ANSI 58. Confirm which arsenic form was tested and the applicable feed concentration, water chemistry, pressure, capacity and maintenance conditions.
WaterMark certification indicates compliance with applicable plumbing-product requirements. It does not, by itself, verify arsenic reduction.
Choose treatment from laboratory results
Use a suitably accredited laboratory to test for total arsenic and determine whether arsenic speciation is needed. The Australian Drinking Water Guidelines health-based value for arsenic is 0.01 mg/L, equivalent to 10 micrograms per litre.
The laboratory or treatment specialist may also need to consider pH and other water characteristics that can affect membrane performance or shorten the life of arsenic-specific media. For private supplies, use a NATA-accredited laboratory whose scope covers the required arsenic analysis and follow current NSW Health guidance. Sydney Water customers can also check the provider’s current published water-quality results.
When another treatment may be better
Oxidation followed by arsenic-specific adsorption or professionally selected ion exchange may be more suitable when As(III) is present, RO is unsuitable or the full water supply needs treatment. Oxidation converts As(III) to the more readily treated As(V); a membrane or suitable media must then capture it.
Iron-based media, activated alumina and anion exchange can remove arsenic in suitable conditions, but performance and service life depend on water chemistry, flow and treatment volume. These systems require professional selection rather than DIY sizing.
Confirm performance and maintain the system
Test the treated water after commissioning and before relying on it. Replace membranes, cartridges or media according to the system’s validated instructions, and retest at intervals appropriate to the source-water risk. Taste, smell and appearance cannot confirm arsenic removal.
Have fixed systems installed by a licensed plumber in accordance with applicable NSW requirements and the manufacturer’s instructions, using WaterMark-certified products where required. Do not modify pressurised pipework yourself. If arsenic is detected, our Sydney plumbing team can help arrange an appropriately specified and installed system.