Discoloured Water & Manganese

Discoloured Tap Water

Firstly, please be assured that your water is not actually ‘dirty’ (in the usual sense of the word). All our water supply systems are closed, meaning that treated water is protected from environmental contaminants, such as soil, groundwater and animal droppings. Clear water storages are lined and covered, and water mains are fully enclosed and operated under pressure such that if there are any undetected pipework cracks, the outward force of the flowing water within the main will prevent the entry of external dirt and groundwater (that is, a leak will be outwards, not inwards).

Tap water appearing a range of colours from yellowish/brown through to brownish/black, and sometimes containing sediments, is actually due to the presence of manganese and other minerals (such as iron) that accumulate within tanks and pipes.

Under normal conditions of flow through a distribution system, the majority of customers will experience few or no discoloured water issues in relation to these sediment build-ups. Some customers who are supplied from regions of the distribution system where water usage is low and sediments tend to collect most (at the ends of courts, for example) may experience issues more frequently.

Occasionally, there are instances of discoloured water being supplied to customers across a widespread area. This is usually the result of sudden changes in pressure or direction of flow through the system causing sediments to dislodge and be stirred up. Such changes occur following mains breaks or simply through sharp increases in water usage.

The information below provides more detail about;

•  What Is Manganese
• Health Effects of Manganese
• Concentrations of Manganese in Water Supply
• Manganese Occurs in a Dissolved and Suspended State
• Oxidation
• Removal & Prevention of Manganese
• Manganese and Laundry Stains
• Water Supply Network Cleaning
• Water Quality Sampling and Testing
• What To Do If You Have Problems With Tap Water Quality

What is 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 South Gippsland’s small local water supply systems.

Health Effects of Manganese

While we do not advise drinking water that is brown in colour, manganese is regarded as one of the least toxic metals when ingested 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 South Gippsland Water must meet the Australian Drinking Water Guidelines and The Safe Drinking Water Act regulations.

Safe Drinking Water Act 

Australian Drinking Water Guidelines

Concentrations of Manganese in Water Supply

Typical concentrations of manganese in South Gippsland Water’s river and reservoir water ranges from 0.003 mg/L to 3.0 mg/L, while in treated drinking water supplies it is under 0.02 mg/L

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”.

South Gippsland Water 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.

South Gippsland Water works to remove as much manganese as possible through both chemical treatment and filtratio

n, 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 Occurs in a Dissolved and Suspended State

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 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 South Gippsland Water’s treatment plants.

Oxidation

When an atom or compound is oxidized (combined with oxygen), its properties change. For example, when an iron object undergoes oxidation, it is transformed because it has lost electrons.  For Manganese the process of oxidation transforms the manganese from its soluble state into a solid state of dark brown through to black sediment particles.

Removal & Prevention of Manganese

South Gippsland Water 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. More vigorous air scour cleaning is also conducted every two or three years (or more frequently if required) for each supply system

Manganese and Laundry Stains

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.  South Gippsland Water can supply you with a product to add to the water to prevent staining.

Water Supply Network Cleaning

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 in two ways;

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.

Air Scouring:  This process utilises a combination of both pressurised air and water to clean or ‘scour’ the sides of the pipe network.  This process takes longer and causes disruption to customers’ services, but uses less water.

The process of both flushing and air scouring 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.

Water Quality Sampling and Testing

South Gippsland Water keeps a close eye on water quality. Water is sampled and analysed through all stages of collection, treatment, storage and distribution to your home. On-line devices continually monitor important water quality indicators, with many being programmed to alarm and shut down treatment plants automatically if specific operating limits are breached. Trained treatment operators also monitor water quality on a daily basis to ensure on-line analysers are working correctly, and so that adjustments can be made to treatment processes as required.

In addition, samples are collected from across the water supply systems on a weekly basis and sent to an external laboratory in Melbourne for independent analysis. Results for regulated parameters are checked by the Department of Health every month. This is to ensure we are meeting strict requirements of safe drinking water legislation.

Water Quality Testing Regime – regulated parameters:

What should I do if I have problems with my tap water quality?

 Please contact us. 1300 851 636 – Our call centre is available 24 hours a day, 7 days a week

 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.