Perth Water Hardness & Quality Report (2026)

Perth's drinking water is supplied by the Water Corporation, drawn from a combination of the Gnangara Mound limestone groundwater system, Jandakot Mound aquifer, and surface reservoirs including Mundaring Weir, supplemented by desalination at the Kwinana and Southern Seawater plants in Western Australia. Water hardness in Perth is measured at 230 mg/L — classified as hard and exceeding the Australian Drinking Water Guidelines (ADWG) aesthetic guideline of 200 mg/L published by NHMRC.

Perth's hardness stems primarily from its reliance on the Gnangara Mound — a vast unconfined aquifer where groundwater moves slowly through Tamala Limestone and the Superficial formation of the Swan Coastal Plain. Calcium carbonate dissolves readily as water percolates through this porous limestone, resulting in elevated mineral concentrations. As Perth's groundwater levels have declined due to reduced rainfall, desalinated water now forms a growing share of the supply blend, though overall hardness remains high.

Perth residents deal with significant limescale accumulation on taps, shower screens, and in kettles — weekly descaling of small appliances is common in many households. Solar hot water systems, widely installed across Perth for their energy savings in the sunny climate, are particularly vulnerable to scale build-up inside the tank and collector tubes, reducing efficiency; annual servicing is strongly recommended. Evaporative coolers — popular in Perth's dry summers — also accumulate heavy mineral scale on evaporative pads, which should be cleaned or replaced each season. Under WA water restrictions, households are encouraged to reduce garden irrigation frequency to two days per week.