Fish River Supply Scheme - Discolouration

Fish River Supply Scheme - Discolouration

Discoloured water within Fish River Supply Scheme

WaterNSW and Lithgow City Council have been investigating reports of discoloured water within the Fish River Water Supply scheme received after a recent pipe break near Sodwalls, which required WaterNSW to shutdown water supply in order to complete the necessary repairs.

Discoloured water can be caused by various reasons and is a typical occurrence after pipes burst and are repaired. The repair work required the pipe to be emptied of water. The subsequent changes to flow direction, coupled with the intensity of flows that occur during repairs and system recharge (where we refill the pipes with water) can disturb natural sediment (mostly manganese and other minerals, such as iron) that accumulate over time in the pipes and tanks. These minerals can cause decoloured water being supplied to customers taps as it is carried through the system.

While we were confident it was the repair work that affected the system, we took water samples from across the Fish River Water Supply Scheme to confirm that this was the root cause of the discolouration and to ensure the safety of the water supply was not compromised.

As expected, extensive water sampling shows that the recent pipe break near Sodwalls has stirred up the natural sediment that entered the Fish River pipeline, which, in turn, has entered reservoirs across the network.

Reports of ongoing discolouration

Testing at Oberon Dam and Duckmaloi WTP have shown increased levels of manganese in the water supply. Manganese is an element that occurs naturally in soil and water and can accumulate at the bottom of dams and other bodies of water.

While manganese is commonly found in water, it is usually avoidable as it is located low in the body of water. However, due to cold temperatures causing the lake to mix at Oberon Dam, manganese is currently present throughout the lake. When dam levels are high, we can test the water at different depths and choose the water with the least manganese. Unfortunately, when dam levels are low, as is the case at Oberon Dam, we do not have as much water, making it harder to avoid depths containing high levels of manganese.

The recent pipe break further exacerbated the situation when the recharging of the system dislodged some of the manganese that had naturally accumulated within the pipes over the years and pushed it through the system.

While the WaterNSW treatment plant removes some manganese, when levels increase in the raw water, some manganese can enter the water system.

WaterNSW and Lithgow City Council drinking water supply must meet the Australian Drinking Water Guidelines . Onsite testing has shown that there is sufficient chlorine and no pathogens present in the water supply, and that trace metals are present in the supply at levels below health limits in the Australian Drinking Water Guidelines.

Although the water is considered safe to drink, we recommend not consuming any water that has an odour or discolouration, and allowing water to flush until it runs clear with no odour before consuming.

Should any customers have persistent issues with discoloured water, it is important to let us know:

Contact WaterNSW on 1300 662 077.

Contact Lithgow City Council on 6354 9999.


Manganese (Mn) is an element that is found in air, soil, and water. It is one of the most abundant metals in the Earth’s crust and is a component of over 100 minerals.

Manganese is an element that occurs naturally in rocks, soils and it is commonly found in the rivers and streams supplying water to WaterNSW customers across NSW.

Manganese can cause discolouration – typically a yellow to brown colour, although occasionally, when manganese oxidises, it can appear as a brownish/black deposit that can cause black films in pipes which can be drawn through the tap.

The term oxidise simply means that an element of compound has been combined with oxygen. For Manganese the process of oxidation transforms the manganese from its soluble state into a solid state, creating a film that visually can range from dark brown through to black.

The levels of manganese present are not harmful to humans but can impact taste, odour and cause discolouration.

While the WaterNSW treatment plant removes some manganese, when levels increase in the raw water, some manganese can enter the water system.

Additionally, some of this manganese will oxidise within the supply network over time, making it possible, in certain situations, to push additional manganese into the network.

WaterNSW is currently investigating additional water treatment options to assist in the removal of manganese.

We are conducting a detailed review of the supply system to investigate the longer-term discolouration issues that have been reported.

We are looking into treatment options to address the issues with discoloured water.

The Fish River Scheme was constructed between the 1940’s and 1960’s. In recent years WaterNSW has progressively upgraded the ageing network to address reliability issues as demand on the network has increased.


Wednesday 12 May
2,553,775 ML
2,581,850 ML
9,233 ML
1,319 ML
87,879 ML
Wednesday 12 May