How do we treat catchment water to make it drinkable?

Most of us are lucky that when we turn on the tap, spotless, protected and high-quality water flows out.

But Senate inquiry for the presence of PFAS, i.e. “forever chemicals”, once again puts the safety of our drinking water in the spotlight.

Lidia Thorpe, independent senator leading the inquiry, says Elders in the Wreck Bay Aboriginal community in Modern South Wales are “purchasing bottled water from aged care packages” due to concerns about the health impacts of PFAS in drinking water.

So how is water deemed protected to drink in Australia? And why does water quality vary in some areas?

This is what happens between the water intake and the tap.

Human interference in the water cycle

There is no “novel” water on Earth. The water we drink can be up to… 4.5 billion years and is constantly recycled in the process hydrological cycle. In this way, water moves from the ground to the atmosphere through evaporation and back (for example through rain).

Humans disrupt this natural cycle by retaining and diverting water from various sources for employ. A lot happens before it reaches your home.

Water quality after turning on the tap depends on a number of factorsincluding the local geology, the type of activities taking place in the catchments and the different processing methods used to process it.

How do we decide what is protected?

The Australian Drinking Water Guidelines define what is considered protected and good quality drinking water.

The guidelines define water quality limits for over 250 physical, chemical and bacterial contaminants. They take into account the potential impact of drinking a pollutant on lifelong health, as well as aesthetics – the taste and color of water.

The guidelines are not mandatory but provide a basis for determining whether the quality of water supplied to consumers in all parts of Australia is protected to drink. Guidelines are constantly changing to ensure they reflect the latest scientific evidence.

From the water intake to the tap

Australians’ drinking water comes mainly from natural catchments. Sources include surface water, groundwater and seawater (via desalination).

Public access to these areas is usually narrow to maintain optimal water quality.

Water is filtered and purified naturally in catchments as it passes through soil, sediment, rocks and vegetation.

However, water from the catchment area is subject to further purification through standard processes which usually focus on:

• removal of solid particles (e.g. soil and sediment)

• filtration (to remove particles and their impurities)

• disinfection (for example, using chlorine and chloramine to kill bacteria and viruses)

• adding fluoride to prevent tooth decay

• adjusting pH to balance water chemistry and facilitate filtration.

This water is supplied to our taps through a mesh system – a network of underground tanks, pipes, pumps and fittings.

In areas where there is no reticulated system, drinking water can also be obtained from rainwater tanks. This means that the quality of drinking water may vary.

There may be sources of contamination roof catchments feeding rainwater tanks and also from the tap because of lead in plumbing fittings and materials.

So does all water meet these standards?

Some rural and remote areas, especially First Nations communities, rely on poor quality surface and underground water
for their drinking water.

Water in rural and regional areas may overflow recommended guidelines for salt, microbial contaminants and trace elements such as lead, manganese and arsenic.

The federal government and other agencies are trying to remedy this.

Destitute water quality in the region has many consequences. These include: implication in increased rate of tooth decay in First Nations people. This happens when access to chilled, sweet drinks is cheaper and easier than access to good quality water.

What about PFAS?

There are also renewed concerns about the presence of PFAS, or “forever” chemicals, in drinking water.

Recent research examining the toxicity of PFAS chemicals along with their presence in some drinking water catchments in Australia and abroad led to a recent assessment of contamination of water sources.

A review by the National Health and Medical Research Council (NHMRC) proposed lowering the limits for four PFAS chemicals in drinking water: PFOA, PFOS, PFHxS and PFBS.

The review used publicly available data and found that most drinking water supplies are currently below levels new guide values ​​were proposed for PFAS.

However, PFAS “heated spots” remain where drinking water catchments or other sources (for example, groundwater) have been impacted by activities in which PFAS have been used in industrial applications. Some communities have expressed concerns about the relationship between elevated levels of PFAS in their communities and cancer clusters.

Although some PFAS were identified as a carcinogenit is not certain whether PFAS causes cancer. There is a link is still under discussion.

Importantly, this is shown by assessing exposure levels from all sources in the population PFAS levels are falling meaning the risk of exposure has also reduced over time.

How about removing PFAS from water?

Most drinking water sources are not linked to industrial contaminants such as PFAS. Thus, water sources are generally not affected expensive purification processes such as reverse osmosisthat can remove most waterborne contaminants, including PFAS. These treatments are energy-intensive and high-priced and are based on the latest water quality assessments by the NHMRC won’t be needed.

Even though pollution is everywhere, it is what it is the dose that makes the poison. Very low concentrations of chemicals including PFAS, while undesirable, may not be harmful and complete removal is not guaranteed.