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Many areas in Western Australia are affected by surface staining from groundwater. This staining is the result of on-going evaporation and subsequent concentration of iron hydroxide, and less commonly manganese or calcium oxides. Surface staining by oxides of iron is an aesthetic problem only and does not affect the quality of groundwater irrigation. In some circumstances a film of iron may appear on the water’s surface which can be mistaken for fuel contamination.
Many garden bores pump groundwater with concentrations of iron that are high enough to cause staining. It is difficult to predict the concentration of iron in groundwater before sinking a bore. Dissolved iron (staining) and hydrogen sulphide (odour) are both highly variable in concentration and can occur throughout the Perth metropolitan region. However, acidic iron-rich groundwater is more common at the watertable close to present or past wetlands where inorganic carbon and sulphides are prevalent and the watertable is shallow and contains little or no dissolved oxygen.
The accuracy of the iron staining risk map is determined by the number of sampled monitoring bores and is therefore highly variable. A high density of monitoring bores is generally associated with well-developed suburbs. A reduction in the density occurs in the outlaying areas of Perth, such as those locations close to the Darling Scarp, or in the south. The mapping does not include all locations that may have iron staining potential.
We recommend checking with neighbours to see if they have experienced iron problems with their bores. Old or damaged galvanised steel pipe-work may add to iron staining problems as acidic waters attack pipe walls.
The unsightly staining may be greatly limited by designing the irrigation system to water only the laws and gardens and not wet pavements, fences and walls.
The Department’s Water Quality Protection Note No. 21 Iron Staining Caused by Irrigation Systems provides guidance on minimising and treating iron staining derived from groundwater irrigation.
For more information call our office on (08) 6364 7600 or see www.water.wa.gov.au/urban-water/drinking-water/protecting-water-quality.