Climate change and drinking water

Anthony Amis

From Chain Reaction #126, April 2016, national magazine of Friends of the Earth, Australia

Climate change is already impacting on the quality of water supplies across Australia. For example, costly desalination plants worth billions of dollars have been rolled out across Australia since 2005 to deal the envisaged future water shortages.

Water supplies to both urban and regional centres have also been threatened by a serious of climate change related events. The biggest threats to drinking water posed by climate change are unusually long droughts, followed by fire and then flooding rains.

Flooding rain occurring after extended dry periods can stir up nutrients in reservoirs and surrounding catchments, which in turn can lead to algal blooms. Algal blooms then require additional and sometimes costly treatment by water authorities.

Perhaps the most serious event of this type occurred in August-September 2007 when a 58 km algal bloom spread over Sydney's Warragamba Dam making a large percentage of the water undrinkable. Toxic Mycrocystins were detected and water had to be treated with powder activated carbon.

Low flows in natural waterways can also be a source of algal blooms. For several months in 2010 water authorities along the Murray River had to contend with extensive blooms of blue green algae. Powder activated carbon dosing was also required to deal with the bloom. Cyanotoxins (blue green algae) can be lethal if ingested.

South East Queensland Water had to pay additional millions of dollars to deal with sediment washed into Wivenhoe Dam by the 2011 January floods. Additional amounts of aluminium based flocculants were required to deal with the very fine sediment particles that had entered the dam.

High levels of aluminium have been linked to Alzheimer's disease. Some of the highest amounts of aluminium recorded in Australia were at Hamilton in western Victoria in July 2008, due to water treatment facilities unable to handle poor quality source water due to drought. Additional water treatment chemicals required to deal with the consequences of climate change could therefore increase health risks, particularly in many vulnerable smaller communities.


Bushfires also threaten water supplies by causing ash, muddy water, heavy metals, phosphorus and fire fighting chemicals to enter reservoirs. Severe fires can burn riparian zones and leave no protection for soils. If heavy rainfall occurs after bushfires, serious erosion and sedimentation problems can eventuate, once again placing pressure on water treatment plants.

Following the 2003 North East Victorian bushfires, a staggering turbidity level of 123,000 Nephelometric Turbidity Units, 24,600 times above the Australian Drinking Water Guidleline, was recorded at Buckland after flash flooding. The Buckland River flows into the Ovens River, which provides drinking water to the town of Wangaratta.

Fish kills were widespread and a turbidity level 7000 times higher than the Australian Drinking Water Guidleline was recorded at Myrtleford, 25 km downstream of Buckland. The poor water quality lead to water restrictions, where water had to be trucked in to dilute water extracted from the Ovens River. Ongoing rainfall meant more sediment entered Ovens River well after the bushfire had occurred.

Disinfection by-products

With treatment plants having to cope with a range of potentially dangerous substances such as viruses, pathogens and bacteria, the pressure to disinfect water by increasing chlorine can also cause potential problems. As water becomes more salty and water levels in reservoirs drop, chlorine used as a disinfectant can react with these organic molecules to create disinfection by-products (DBPs). Some DBPs have been linked to bladder cancer. Higher water temperatures can also cause disinfection by-product problems, including water supplied via pipelines. In October 2012 Friends of the Earth revealed that many thousands of people in South Australia, including suburbs of Adelaide, had been exposed to drinking water with high levels of the Trihalomethane, Bromodichloromethane, in some areas for over a decade.

Many small communities in Victoria's Wimmera region, who source their drinking water from the Grampians, suffered high levels of chlorine DBPs during the millennium drought of the 2000s. A severe water shortage was experienced across the region, with the capacity of some of the regions headwork reservoirs falling as low as 2.5%. The prolonged drought meant that communities who were reliant on water being channelled to their communities from the headwork reservoirs found that this could not occur, and were left with older water which had been retained in their town storages. This water became more saline and the salinity directly impacted on the concentration of DBPs produced.

Following the DBP problem, in January 2011, heavy rain caused 200 landslips in the Grampians including many in the Lake Bellfield catchment, the major water supply catchment in the region. The catchment had also been severely burnt by bushfires in 2006. Severe sedimentation problems eventuated. Ten thousand people in 19 communities were impacted as their communities did not have water treatment plants to treat the sediment. Water supplies to many of the regions towns were undrinkable between 2011-12. A new range of DBPs was also formed as a result of the erosion problems.

As a way to reduce DBPs, water authorities sometimes add ammonia to chlorine as a means of extending the lifetime of the disinfectant. This treatment is known as chloramination. Chloraminated water can cause some health problems and aggravate others such as skin, digestive and respiratory ailments. Residents from the Victorian town of Maryborough have recently been in contact with Friends of the Earth regarding the poor quality of their recently chloraminated drinking water supply. The region recorded high levels of the DBP trihalomethanes (most notably Bromoform) between January 2007 and January 2009. Source water from nearby Tullaroop Reservoir had fallen dramatically. Since chloramination, the DBPs have significantly decreased, but now the community faces chloramination concerns. This scenario will also play out across many regional centres across Australia in the following decades as they make the switch to chloramination.