2004/18: Wiluna (Western Australia). Nitrate, Hardness, Total Dissolved Solids, Silica

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Wiluna (Western Australia) – Nitrate

“Cue, Meekatharra, Mount Magnet, New Norcia, Sandstone, Wiluna and Yalgoo have been granted an exemption from compliance with the nitrate guideline by the Department of Health. The water supplied is harmless to adults and children over the age of 3 months of age. Carers of infants younger than three months should seek advice from the Community Health Nurse regarding the use of alternative water sources for the preparation of bottle feeds. The Water Corporation provides bottled water free of charge for this purpose.” Water Corporation WA 2004/5 Annual Water Quality Report

Nitrate: ADWG Guideline 50mg/L. Nitrate is the product of oxygenated nitrogen created from the breakdown of organic matter; lightning strikes; inorganic pesticides; or explosives. The Australian Drinking Water Guidelines recommend that nitrate levels between 50-100mg/L are a health consideration for infants less than three months, although levels up to 100mg/L can be safely consumed by adults. Mainly a problem in Northern Territory and some communities in Western Australia.

Wiluna – Western Australia – Hardness

2007/08: Wiluna (Western Australia) – Hardness 365mg/L (Highest Detection Only)

2008/09: Wiluna (Western Australia) – Hardness 360mg/L (max), 300mg/L (mean)

2010/11 Wiluna (Western Australia) Hardness 220mg/L (max), 185mg/L (av)

2011/12 Wiluna (Western Australia) Hardness 250mg/L (max), 180mg/L (av)

2013/14 Wiluna (Western Australia) Hardness 240mg/L (max), 235mg/L (av)

2014/15 Wiluna (Western Australia) Hardness 320mg/L (max), 280mg/L (mean)

GUIDELINE

“To minimise undesirable build‑up of scale in hot water systems, total hardness (as calcium
carbonate) in drinking water should not exceed 200 mg/L.

Hard water requires more soap than soft water to obtain a lather. It can also cause scale to form on hot water pipes and fittings. Hardness is caused primarily by the presence of calcium and magnesium ions, although other cations such as strontium, iron, manganese and barium can also contribute.”

Australian Drinking Water Guidelines 2011

Wiluna – Western Australia – Total Dissolved Solids

2008/09: Wiluna (Western Australia) – Total Dissolved Solids 815mg/L (max), 716mg/L (mean)

2010/11 Wiluna (Western Australia) Total Dissolved Solids 610mg/L (max), 561mg/L (av)

2011/12 Wiluna (Western Australia) Total Dissolved Solids 663mg/L (max), 558mg/L (av)

2013/14 Wiluna (Western Australia) Total Dissolved Solids 660mg/L (max), 656mg/L (av)

2014/15 Wiluna (Western Australia) Total Dissolved Solids 783mg/L (max), 734mg/L (mean)

GUIDELINE

“No specific health guideline value is provided for total dissolved solids (TDS), as there are no
health effects directly attributable to TDS. However for good palatability total dissolved solids
in drinking water should not exceed 600 mg/L.

Total dissolved solids (TDS) consist of inorganic salts and small amounts of organic matter that are dissolved in water. Clay particles, colloidal iron and manganese oxides and silica, fine enough to pass through a 0.45 micron filter membrane can also contribute to total dissolved solids.

Wiluna (Western Australia) – Silica

2013/14 Wiluna (Western Australia) Silica 85mg/L (max), 82.5mg/L (av)

2014/15 Wiluna (Western Australia) Silica 85mg/L (max), 85mg/L (mean)

2015/16 Wiluna (Western Australia) Silica 90mg/L (max), 87.5mg/L (mean)

2016/17 Wiluna (Western Australia) Silica 85mg/L (max), 82.5mg/L (mean)

2017/18 Wiluna (Western Australia) Silica 85mg/L (max), 85mg/L (mean)

To minimise an undesirable scale build up on surfaces, silica (SiO2) within drinking waters should not exceed 80 mg/L.
GENERAL DESCRIPTION
Silica present in water is usually referred to as amorphous silica (i.e. lacking any crystalline structure). When silica is dissolved within water it forms monosilicic acid:
SiO2 + 2H2O à Si(OH)4
When the concentrations of monosilicic acid increase, polymerisation of the silica occurs, forming polysilicic acids followed by formation of colloidal silica. Monosilicic acid and polysilicic acids are the forms of silica analysed when determining dissolved silica content.
The deposition of silica from solutions can occur via various mechanisms. The deposition of silica that can cause the most problems for the water industry is via silica’s ability to deposit on solid surfaces that have hydroxyl (OH) groups present. Surfaces that commonly have hydroxyl groups present are glass and metallic surfaces. For example, dissolved silica will react with the surfaces of glass and begin to form a white precipitate. The silica forms silicates on the surface, resulting in silica build-up. In cases where customer complaints occur due to scale build-up, water hardness and silica concentrations should be investigated to determine the cause.
Silica can be a problem in water treatment due to its ability to cause fouling of reverse osmosis (RO) membranes (Sheikholeslami and Tan, 1999, Ning 2002, Sahachaiyunta and Sheikholeslami 2002). This occurs when the dissolved silica of the concentrate becomes super-saturated, causing silicates to form in the presence of metals, and these deposit on the membrane surface. The silicate then dehydrates, forming hard layers on the membrane that reduce the effectiveness of the process… 2011 ADWG