Treatment
Water treatment plants – making safe water
Two types of ‘raw’ or untreated water are used by Hunter Water:
- surface waters from Chichester and Grahamstown Dams
- ground waters from Tomago and Tomaree sandbeds.
Untreated water from the Tomaree sandbeds needs only disinfection, fluoridation and pH adjustment to make it safe for drinking.
However, water from Chichester, Grahamstown and Tomago contain some naturally present impurities. For example, the raw water may contain particles including clays and silts, natural organic matter, iron and manganese, and micro-organisms. In addition, the natural pH of the water may need adjustment.
Why untreated water can not be used
The following table shows the problems with using untreated drinking water, as specific impurities, or components, have different effects on the composition of the water:
| Component |
Effect |
| Clays and Silts |
‘Cloudy’ unaesthetic water, and particles can shield micro-organisms from disinfection |
| Natural Organic Matter |
Taste and odour problems |
| Iron |
Taste and odour and aesthetic problems |
| Manganese |
Taste and odour and aesthetic problems |
| High or Low pH |
Can cause problems with corrosion, taste and odour problems, and ineffective disinfection |
| Micro-organisms |
Removal of Pathogenic micro-organisms is necessary to prevent water-borne illness |
Hunter Water meets all guidelines for drinking water
Drinking Water should be safe to use and aesthetically pleasing. It should be clear and colourless, with no unpalatable taste or odour, and it should contain no suspended matter, harmful chemical substances or pathogenic micro-organisms.
Hunter Water supplies high quality drinking water to its customers. Drinking Water supplied by Hunter Water is regularly tested throughout the distribution system, and complies with the National Health and Medical Research Council (NHMRC) Australian Drinking Water Quality Guidelines. Available on-line at http://www.nhmrc.gov.au/publications/synopses/eh19syn.htm
The NHMRC Guidelines set out requirements for microbiological, physical and chemical requirements for drinking water. Guidelines for key parameters are summarised below and you can see that Hunter Water’s drinking water meets these standards:
Summary of 2004 NHMRC Drinking Water Guidelines – Key Parameters
| Category |
Parameter |
Guideline |
HWC Drinking Water Average Jul 2005 – Jun 2006 |
| Physical |
Turbidity |
< 5 NTU |
0.4 NTU |
| |
pH |
6.5 to 8.5 |
7.8 |
| |
Colour |
< 15 HU |
5 HU |
| Chemical |
Iron |
< 0.3 mg/L |
0.02 mg/L |
| |
Manganese |
< 0.1 mg/L |
0.01 mg/L |
| |
Aluminium |
< 0.2 mg/L |
0.045 mg/L |
| |
Copper |
< 1 mg/L |
0.02 mg/L |
| |
Lead |
< 0.01 mg/L |
0.0011 mg/L |
| |
Zinc |
< 3 mg/L |
0.02 mg/L |
| |
Fluoride |
<1.5 mg/L |
<0.94 mg/L |
| |
Chlorine |
< 5 mg/L |
0.3 mg/L |
| |
Trihalomethanes (Disinfection by-product) |
< 0.25 mg/L |
0.064 mg/L |
| Microbiogical |
E.Coli |
98% of samples shall contain no E.Coli |
99.6% of samples contained no E.ColiWater treatment plants |
How our water treatments work
Hunter Water ensures we meet the required drinking water guidelines by following a careful treatment process at our water treatment plants. Water treatment plants are also known as Water Filtration Plants and ours are located at:
The treatment process may vary slightly at different locations, depending on the technology of the plant and the water it needs to process, but the basic principles are largely the same. This section describes a standard water treatment process.
Figure 1 Typical Process Flow Diagram
Coagulation / Flocculation
During coagulation, liquid aluminium sulfate (alum) and/or polymer is added to untreated (raw) water. When mixed with the water, this causes the tiny particles of dirt in the water to stick together or coagulate. Next, groups of dirt particles stick together to form larger, heavier particles called flocs which are easier to remove by settling or filtration.
Sedimentation
As the water and the floc particles progress through the treatment process, they move into sedimentation basins where the water moves slowly, causing the heavy floc particles to settle to the bottom. Floc which collects on the bottom of the basin is called sludge, and is piped to drying lagoons. In Direct Filtration, the sedimentation step is not included, and the floc is removed by filtration only.
Filtration
Water flows through a filter designed to remove particles in the water. The filters are made of layers of sand and gravel, and in some cases, crushed anthracite. Filtration collects the suspended impurities in water and enhances the effectiveness of disinfection. The filters are routinely cleaned by backwashing.
Disinfection
Water is disinfected before it enters the distribution system to ensure that any disease-causing bacteria, viruses, and parasites are destroyed. Chlorine is used because it is a very effective disinfectant, and residual concentrations can be maintained to guard against possible biological contamination in the water distribution system.
Sludge Drying
Solids that are collected and settled out of the water by sedimentation and filtration are removed to drying lagoons.
Fluoridation
Water fluoridation is the treatment of community water supplies for the purpose of adjusting the concentration of the free fluoride ion to the optimum level sufficient to reduce dental caries. Hunter Water is required to fluoridate water in accordance with the NSW Fluoridation of Public Water Supplies Act 1957.
pH Correction
Lime is added to the filtered water to adjust the pH and stabilise the naturally soft water in order to minimise corrosion in the distribution system, and within customers’ plumbing.
Take our virtual tour of HWC water treatment processes
Start Tour