Water Quality and Treatment

The quality of our water varies, especially in summer. We have 10 treatment plants across the region, which carefully clear the water to make it safe for drinking or river quality services.

For further information, read the latest Annual Drinking Water Quality Report.

Coagulation and Flocculation

The first step of the conventional treatment process involves dosing a chemical coagulant to help gather suspended solids and organic material in the raw water. We use Aluminium Sulphate and Aluminium Chlorohydrate to bring about the coagulation process, which helps to form larger particles called ‘flocs’ which can be removed more readily by subsequent treatment steps. During flocculation, the floc particles develop to a larger size. The larger size and weight of the floc then assists in the sedimentation process. Flocculant aids including polyelectrolytes are also commonly used to enhance the flocculation phase which further assists in the sedimentation process.


The purpose of sedimentation is to enhance the filtration process by removing particulates. Sedimentation is the process by which suspended particles are removed from the water by means of gravity or separation. In the sedimentation process, the water passes through a relatively quiet and still basin. In these conditions, the floc particles settle to the bottom of the basin while “clear” water passes out of the basin over an effluent baffle or weir. The solids collect on the basin bottom and are removed by a mechanical “sludge collection” device which scrapes the solids (sludge) to a collection point within the basin from which it is pumped to disposal or to a sludge treatment process.

Solid Contact Clarification

The purpose of the solid contact clarification is the same as the sedimentation process i.e. to enhance the filtration process by removing particulates. It involves mixing the influent flow with previously settled solids within a cylinder located in the centre of the clarifier. Gentle mixing within the reaction well promotes agglomeration of floc particles and/or chemical precipitates. The aggregated solids settle out more rapidly in the clarification area. Even better clarity is achieved when particles become enmeshed in a sludge blanket layer. Rotating sludge scrapers transport settled solids to the centre of the basin for removal. Clarified overflow is removed through a circular launder system that draws water from the entire surface area to prevent solids carryover caused by uneven velocity currents.

Diffused Air Floatation

The process of flotation consists of three steps:

  • Bubble formation
  • Attachment of bubbles to the solids
  • Solids separation from the fluid

In DAF systems, air is pressurised under several atmospheres and then introduced into water, where it’s mixed with pre-coagulated water just before it enters the flotation tank.
Upon attachment of air bubbles to the solid particles, the density of the solid becomes less than that of the surrounding fluid. In the process, the buoyant force lifts the solids to the surface to form a scum blanket, which is continuously swept to the periphery, automatically discharged into a scum trough by the skimming device.


Filtration occurs as the water passes through filters that help remove particles that have not settled in the sedimentation process. Sand filters are commonly used in the water treatment process and may contain layers of gravels, sands and filter coal. The sand filtration process removes fine suspended solid matter as well as some other particles including larger micro-organisms, resulting in clear water passing through.


Water is disinfected to kill any pathogens (disease-causing organisms) that remain in the treated water after filtration and provide protection within the distribution system. Without disinfection, the risk from waterborne disease is greatly increased. Disinfection is carried out by chlorination at all our water treatment plants in the form of Chlorine gas.

pH correction

Due to the addition of coagulants and chlorine, the pH (acidity) of the water being treated is lowered, becoming more acidic. To inhibit corrosion and make the water safe to use, the pH is adjusted to a neutral pH, about pH 7.0, by adding lime or other alkaline chemicals such as soda ash or sodium hydroxide.


Water fluoridation is the adjustment of fluoride in drinking water to a level that helps protect teeth against dental decay. We fluoridate 11 of our drinking water supplies. Fluoridation of the drinking water supplies is undertaken as per requirements of the Health (Fluoridation) Act 1973.

Non-potable (untreated) water supplies

A requirement of the Safe Water Drinking Act is to ensure that customers and visitors in areas receiving non-potable water understand that it is untreated and therefore not suitable for consumption.

In response to this requirement, we have produced a pamphlet titled ‘Living with an Untreated Water Supply’. The pamphlet cautions that untreated water is not fit for such things as drinking, food preparation or cleaning teeth. It also advises customers to take care when bathing and showering.

The pamphlet is made available to new customers receiving a non-potable supply.  We also provide reminders to existing customers every 2 years by way of social media, newspaper advertising and a note with their quarterly account.

Water Quality Standard

The water quality must also meet the requirements of the Safe Drinking Water Act 2003 (SDWA).

All of our treatment plants treat the water to comply with the Australian Drinking Water Guidelines  (ADWG), which is the standard required by the Victorian Government.

You can find the current guidelines in the link below:

Monitoring and Testing

We monitor our water to ensure that the water delivered to our customers meets ADWG guidelines and the SDWA. Samples are collected as water leaves the treatment plants and customer taps, in accordance with the requirements of the SDWA. An independent laboratory that is accredited by the National Association of Testing Authorities (NATA) and approved by the Department of Human Services, tests the water samples.

Types of testing:

Microbiological tests

Water is tested to ensure that it is free from micro organisms that can cause disease. These tests measure the presence of E.Coli and the total number of coliforms, or bacteria, which indicate possible contamination from sources such as human or animal waste. Tests are also conducted for Cryptosporidium or Giardia.

Physical and Chemical Tests

The physical characteristics of water relate to its appearance, taste, odour and ‘feel’, as well as the corrosion or scaling potential of the water. Physical tests conducted include tests for colour, turbidity and pH. The pH is a measure of whether the water is acidic or basic. A pH of 7 is neutral. Turbidity is a measure of the number of particles present in the water, thus high turbidity causes a cloudy appearance.

Chemical tests are conducted for a range of substances, including chlorine, and disinfection by-products and aluminium. These tests indicate the presence of substances that may be naturally occurring or added to the water during the treatment process for health or aesthetic purposes. Tests for a range of health-related inorganic and organic components as well as pesticides/herbicides are also undertaken.

Risk Management

A drinking water quality management plan encompassing Hazard Analysis and Critical Control Points (HACCP), is in place for all our urban supplies. HACCP is an internationally recognised system that identifies and manages significant risks at key points in the water production process.