2007/17 + 2021/22 – Gapuwiyak/Lake Evella (Northern Territory) – Lead, pH

Gapuwiyak (Northern Territory) – Lead

2014/15: Gapuwiyak (Northern Territory) – Lead 0.01mg/L (95th %)

Lead Australian Drinking Water Guideline 0.01mg/L

“… Lead can be present in drinking water as a result of dissolution from natural sources, or from household plumbing systems containing lead. These may include lead in pipes, or in solder used to seal joints. The amount of lead dissolved will depend on a number of factors including pH, water hardness and the standing time of the water.

Lead is the most common of the heavy metals and is mined widely throughout the world. It is used in the production of lead acid batteries, solder, alloys, cable sheathing, paint pigments, rust inhibitors, ammunition, glazes and plastic stabilisers. The organo-lead compounds tetramethyl and tetraethyl lead are used extensively as anti-knock and lubricating compounds in gasoline…ADWG 2011

Gapuwiyak (Northern Territory) – pH (acidic)

2007/08: Gapuwiyak pH 5.9

2008/09: Gapuwiyak pH 6

2009/10: Gapuwiyak pH 6.1

2010/11: Gapuwiyak pH 6

2013/14: Gapuwiyak pH 6

2015/16: Gapuwiyak pH 6

2016/17: Gapuwiyak pH 6

2021/22: Gapuwiyak pH 5.8

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.