Discoloured water and manganese

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 commonly found in the rivers and streams supplying water to Armidale Regional Council (ARC) water supply systems.

While we do not advise drinking water that is brown in colour, manganese is regarded as one of the least toxic metals when consumed by oral route (that is, through eating and drinking). It is actually an essential trace mineral required in our diets for good health, and is not harmful when consumed at low concentrations.

Water is safe to drink. Water supplied by Armidale Regional Council must meet the Australian Drinking Water Guidelines.

The National Health and Medical Research Council’s Australian Drinking Water Guidelines (ADWG) states that “based on aesthetic considerations, the concentration of manganese in drinking water should not exceed 0.1 mg/L at the customer’s tap. Manganese would not be a health consideration unless the concentration exceeded 0.5 mg/L”.

ARC finds that the level of soluble manganese in reservoirs fluctuates throughout the year with late spring, summer and autumn when levels are at their highest.

ARC works to remove as much manganese as possible through both chemical treatment and filtration, however, not all manganese can be removed.

Small amounts pass through where they typically form sediments at the bottom of pipes and do not cause problems at customers’ taps, until such time as there is a disturbance in the water pressure or flows.  Usually, these disturbances are from high flows such as a burst water main, the use of standpipes and fire hydrants, or in hot weather when peak water demand occurs.

Manganese may be soluble or insoluble in water depending on its chemical state. When dissolved in water, manganese is not visible and water appears clear. However, when manganese oxidises (combines with oxygen to become an oxide), an insoluble solid is formed which appears as fine, brownish/black sediments.

As such, treatment involves oxidising the mineral using Potassium Permanganate or Sodium Hypochlorite to transform manganese into a solid state so the compound can be removed through filtration.

Because it can be found in both a dissolved and solid state, it is difficult and expensive to completely remove using the technology currently available at the Guyra Water Treatment Plant.

ARC aims to minimise the levels of manganese in treated water supplies as much as possible. In general, this is done by creating conditions that cause soluble manganese in untreated source waters to oxidise before or during the water treatment stages of coagulation and flocculation.

The manganese oxide solids formed can then be physically removed during clarification and filtration processes. Oxidation conditions are achieved by aeration of reservoirs and basins using large mixing devices, and addition of oxidising agents to water as it enters treatment plants.

Not all soluble manganese can be removed in this way and trace levels will remain in treated water. Some of the remaining manganese will oxidise within tanks and pipes, leading to accumulation of sediments over time. To minimise sediment build-ups, flushing of water mains is carried out routinely.

Quite often manganese is noticed in laundry due to the fact that many washing powders use oxidising agents.  When manganese is present in the water on contact with oxygen or these washing powders cause it to oxidise and in fact set brown/black stains in your laundry.

If you are doing laundry and notice that the water contains particles or has a taint to it, leave the laundry items in the machine or tub; do not spin or hang out to dry as this will set stains that may have formed. 

Once Manganese finds its way into a water supply network it requires cleaning of all pipes and storage tanks to remove it. Due to manganese being present in our local water sources year-round, network cleaning is an on-going requirement.  Water pipe cleaning is typically done by;

Flushing:  Water is flushed out of pipes at high volumes to draw sediments out of the pipes. This requires the use of a volume of water but does not cause service disruptions to customers.

The process of flushing often dislodges more sediments, so it is not uncommon for water quality to be impacted during the cleaning process. It sometimes appears that the problem gets worse before an improvement is noticed.

We welcome your call as this not only allows us to attend to your specific issue straight away, but also helps us to identify problem areas. If a water quality issue is widespread, we may request your patience while the problem is addressed. For those people who experience ongoing, occasional issues, we can implement a targeted flushing program to ensure water at your address consistently appears clear and is not unpleasant to taste.

To report an issue please call 1300 136 833 24 hours a day seven days a week.