2007/18 – Grass Patch (Western Australia) – pH, Hardness, Total Dissolved Solids, Silica

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Grass Patch (Western Australia) – pH (alkaline)

Average pH: 2007 July-2008 June: 8.77 pH units

Average pH: 2009 July-2010 June: 8.65 pH units

2010/11 Grass Patch  (Western Australia) pH 8.63 (av)

2011/12 Grass Patch (Western Australia) pH 9.05 (av)

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.

2008/09 – Grass Patch (Western Australia) – Hardness

2008/09: Grass Patch (Western Australia) Hardness 324mg/L (max), 171mg/L (mean)

2009/10: Grass Patch (Western Australia) Hardness 370mg/L (max)

2010/11 Grass Patch (Western Australia) Hardness 370mg/L (max), 238mg/L (av)

2013/14 Grass Patch (Western Australia) Hardness 360mg/L (max), 353mg/L (av)

2014/15 Grass Patch  (Western Australia) Hardness 360mg/L (max), 345mg/L (mean)

2015/16 Grass Patch (Western Australia) Hardness 350mg/L (max), 348mg/L (mean)

2016/17 Grass Patch (Western Australia) Hardness 350mg/L (max), 348mg/L (mean)

2017/18 Grass Patch (Western Australia) Hardness 350mg/L (max), 335mg/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.”

Grass Patch – Western Australia – Total Dissolved Solids

2010/11 Grass Patch (Western Australia) Total Dissolved Solids 884mg/L (max), 652mg/L (av)

2013/14 Grass Patch (Western Australia) Total Dissolved Solids  860mg/L (max), 849mg/L (av)

2014/15 Grass Patch (Western Australia) Total Dissolved Solids 857mg/L (max), 836mg/L (av)

2015/16 Grass Patch (Western Australia) Total Dissolved Solids 885mg/L (max), 854mg/L (av)

2016/17 Grass Patch (Western Australia) Total Dissolved Solids 849mg/L (max), 823mg/L (av)

2017/18 Grass Patch (Western Australia) Total Dissolved Solids 831mg/L (max), 809mg/L (av)

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.

Total dissolved solids comprise: sodium, potassium, calcium, magnesium, chloride, sulfate, bicarbonate, carbonate, silica, organic matter, fluoride, iron, manganese, nitrate, nitrite and phosphates…” Australian Drinking Water Guidelines 2011

2017/18 – Grass Patch (Western Australia) – Silica

2017/18 Grass Patch  (Western Australia) Silica 115mg/L (max), 107.5mg/L (mean) (listed as Silicon in Water Corporation Water Quality Report 2017-18)

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