Rottnest Island – (Western Australia) – Bromate
2020/21 – Rottnest Island (Western Australia) – Bromate 0.031mg/L (maximum)
The health characteristics sampled during the 2020‐2021 reporting period returned results in line with those taken during the 2019‐2020 period, returning five exceedances of bromate compared with three exceedances in the previous reporting period.
Bromate testing was added to the agreed sampling schedule in the 2017‐2018 reporting period. This followed a request from the Department of Health to participate in a voluntary monitoring program for bromate.
Bromate: Regulatory Standard = 0.02mg/L (Also see section of desalination). A suspected carcinogen. Bromate is formed when ozone used to disinfect drinking water reacts with naturally occurring bromide found in source water. Bromate formation in disinfected drinking water is influenced by factors such as bromide ion concentration, pH of the source water, the amount of ozone and the reaction time used to disinfect the water.
Rottnest Island (Western Australia) – Iron
2020/2021: Rottnest Island (Western Australia) – Iron 0.39mg/L (max), 0.07mg/L (mean/av.)
Iron: 9 of the 102 samples recorded iron concentrations above the Australian Drinking Water
Guidelines aesthetic value of 0.3 mg/L, with the highest concentration reported at 0.91 mg/L
at R12/008 in March 2021. All nine of the iron exceedances occurred at R12/008 during the
reporting period. Investigation into the cause of the exceedances are still ongoing.
Iron has a taste threshold of 0.3 mg/L in water, and becomes objectionable above 3 mg/L
Based on aesthetic considerations (precipitation of iron from solution and taste),
the concentration of iron in drinking water should not exceed 0.3 mg/L.
No health-based guideline value has been set for iron.
Iron has a taste threshold of about 0.3 mg/L in water, and becomes objectionable above 3 mg/L. High iron concentrations give water an undesirable rust-brown appearance and can cause staining of laundry and plumbing fittings, fouling of ion-exchange softeners, and blockages in irrigation systems. Growths of iron bacteria, which concentrate iron, may cause taste and odour problems and lead to pipe restrictions, blockages and corrosion. ADWG 2011
Rottnest Island (Western Australia) – pH (alkaline)
2020/21: Rottnest Island (Western Australia) pH 8.69 (mean)
pH: 2 of 120 samples reported pH values outside the Australian Drinking Water Guidelines
aesthetic pH range of 6.5 ‐ 8.5. The exceedances for the 2020‐2021 period were at the
following locations:
R12/002 in July 2020 and August 2020, reported a pH of 8.9 and 8.7 respectively, 0.4 and 0.2
pH units above the Australian Drinking Water Guideline upper limit respectively.
In May 2021, R12/004, R12/006 and R12/008 were reported as having pH below the lower
limit in the Australian Drinking Water Guidelines. Recalibration and retesting by the lab
returned results above the lower limit and are therefore no longer reported as exceedances
within this report
Based on the need to reduce corrosion and encrustation in pipes and fittings, the pH of
drinking water should be between 6.5 and 8.5.
New concrete tanks and cement-mortar lined pipes can significantly increase pH and
a value up to 9.2 may be tolerated, provided monitoring indicates no deterioration in
microbiological quality.
pH is a measure of the hydrogen ion concentration of water. It is measured on a logarithmic scale from 0 to 14. A pH of 7 is neutral, greater than 7 is alkaline, and less than 7 is acidic.
One of the major objectives in controlling pH is to minimise corrosion and encrustation in pipes and fittings. Corrosion can be reduced by the formation of a protective layer of calcium carbonate on the inside of the pipe or fitting, and the formation of this layer is affected by pH, temperature, the availability of calcium (hardness) and carbon dioxide. If the water is too alkaline (above pH 8.5), the rapid deposition and build-up of calcium carbonate that can result may eventually block the pipe.
Rottnest Island (Western Australia) Nickel
2020/21: Rottnest Island (Western Australia) Nickel 0.034mg/L
There was one health exceedance within this reporting period for Nickel at Visitor Centre drinking fountain in August 2020. The source of the exceedance was found to be corroded fittings, which were replaced before the next monitoring round. There were no exceedances following the parts replacement and the drinking fountain was opened for public use in September 2020
Nickel: ADWG Health Guideline 0.02mg/L. A chemical element and silvery white corrosion resistant metal with a golden tinge. 60% of nickel production is used in nickel steel (particularly stainless steel). In water, mainly a problem with nickel plated fittings. Main releases to the environment are from the burning of fossil fuels and in waste discharges from electroplating industries.