A river can look clear and still be chemically stressed. In NSW water management, chemists do not rely on appearance alone. They monitor parameters such as conductivity, dissolved oxygen, pH and coliform bacteria to decide whether water is safe for ecosystems, agriculture and human use.
Use the PDF for classwork, homework or revision. It includes key ideas, activities, questions, an extend task and success-criteria proof.
The Hunter River Salinity Trading Scheme monitors river water so industrial and environmental needs can both be managed. Imagine two river samples:
Which sample would you predict is healthier for aquatic life, and what measurements would you want before making a final judgement?
📚 Core Content
Wrong: Clean water is water with no dissolved substances at all.
Right: Pure water with no dissolved substances does not exist naturally and would be unpalatable and potentially harmful. "Clean" water meets quality standards for specific uses — it contains acceptable levels of dissolved minerals, has safe microbial counts, and is free from toxic contaminants.
Water quality is not one thing. It is a bundle of measurements that together tell chemists whether water is physically suitable, chemically balanced and biologically safe.
When chemists assess water quality, they look at physical parameters such as temperature and turbidity, chemical parameters such as pH, dissolved oxygen, total dissolved solids and conductivity, and biological parameters such as coliform bacteria.
No single parameter gives a complete answer. Clear water may still contain harmful dissolved ions. Neutral pH water may still be oxygen-poor. A full judgement comes from reading the measurements together.
| Parameter | Type | What it measures | Why it matters |
|---|---|---|---|
| Temperature | Physical | Thermal condition of the water | Affects dissolved oxygen and organism survival |
| Turbidity | Physical | Cloudiness from suspended particles | High turbidity reduces light penetration and may indicate runoff |
| pH | Chemical | Acidity or alkalinity | Affects chemical equilibria, toxicity and biological function |
| Dissolved oxygen (DO) | Chemical | Oxygen available in water | Essential for aerobic aquatic life |
| Biochemical oxygen demand (BOD) | Chemical/biological | Oxygen used by microbes to decompose organic matter | High BOD suggests pollution and oxygen stress |
| Total dissolved solids (TDS) | Chemical | Amount of dissolved ions and substances | High TDS affects salinity and water suitability |
| Conductivity | Chemical | Ability to conduct electricity | Indirectly indicates dissolved ion concentration |
| Coliform bacteria | Biological | Indicator of faecal contamination | Suggests microbial safety risk |
Notice that some parameters are direct measurements, while others are indicators. Conductivity does not tell you exactly which ions are present, but it tells you the water contains dissolved charged species in significant amount.
A useful parameter is not just one we can define; it is one we can measure reliably in the field or laboratory.
The method chosen depends on speed, required accuracy and the question being asked. Field monitoring often favours fast probe-based measurement, while compliance testing may require more formal laboratory methods.
A number on its own is not enough. Water-quality data become meaningful when compared with standards or acceptable ranges for human and environmental safety.
The Australian Drinking Water Guidelines (ADWG) provide guidance on acceptable drinking-water quality. These guidelines are based on protecting human health as well as managing aesthetic factors such as taste, odour and appearance.
For environmental monitoring, acceptable ranges can differ depending on the ecosystem and use of the water. A value that is acceptable in one context may be concerning in another, which is why chemists must interpret standards in context rather than as isolated numbers.
Water-quality interpretation becomes much more powerful when you can explain not just what changed, but why it changed.
Temperature and dissolved oxygen are inversely related: as water temperature increases, dissolved oxygen solubility decreases. This matters ecologically because warm water can place aquatic organisms under oxygen stress even before additional pollution is considered.
This is the real analytical skill in IQ2: reading a pattern of parameters and linking it to a plausible environmental cause.
The temperature effect matters because it lowers the starting oxygen capacity of the water. Warm water therefore becomes more vulnerable to oxygen stress when organic pollution or low mixing is also present.
📊 Data Interpretation
Sample B shows several warning signs at once: higher temperature, higher turbidity, lower dissolved oxygen, higher conductivity and elevated coliform bacteria. This is exactly how real water-quality interpretation works — one concerning result matters, but a pattern of concerning results matters more.
🧠 Activities
1 Temperature
2 Conductivity
3 Coliform bacteria
4 Dissolved oxygen
1 Agricultural runoff after heavy rain
2 Industrial discharge containing dissolved salts and metals
3 Urban stormwater carrying sediment and waste
1. Which of the following is a biological water-quality parameter?
2. How does increasing water temperature affect dissolved oxygen solubility?
3. Which parameter is most directly used as an indicator of dissolved ion load in water?
4. A river sample has high turbidity, elevated coliform bacteria and reduced dissolved oxygen. Which contamination source is most strongly suggested?
5. Why are standards such as the ADWG important in water chemistry?
1. Describe three key parameters used to assess water quality and explain what each one indicates about the condition of the water. 4 marks
2. Explain why warmer water can create ecological problems even before additional pollutants are added. 4 marks
3. Evaluate whether conductivity alone is enough to judge the safety of a river sample in a monitoring program such as the Hunter River Salinity Trading Scheme. 5 marks
Go back to the opening river comparison and upgrade your prediction into a more complete water-quality judgement.
1. Temperature is a physical parameter. It tells the chemist about thermal conditions and helps predict dissolved oxygen behaviour.
2. Conductivity is a chemical parameter. It indicates the presence of dissolved ions and therefore helps assess salinity or contamination by ionic substances.
3. Coliform bacteria is a biological parameter. It indicates possible faecal contamination and microbial safety risk.
4. Dissolved oxygen is a chemical parameter. It matters because aquatic organisms need oxygen for aerobic respiration.
1. Agricultural runoff is likely to increase turbidity and nutrient levels, and may later contribute to oxygen stress.
2. Industrial discharge containing salts and metals is likely to raise conductivity, TDS and possibly alter pH.
3. Urban stormwater is likely to raise turbidity and microbial contamination, and may also increase organic load.
1. C — coliform bacteria is the biological parameter listed.
2. A — increasing temperature decreases dissolved oxygen solubility.
3. D — conductivity is the most direct indicator of dissolved ion load.
4. B — this pattern strongly suggests stormwater or sewage-related contamination.
5. C — standards provide the basis for judging whether measured values are acceptable.
Q1 (4 marks): Temperature indicates thermal conditions and affects dissolved oxygen solubility. Turbidity indicates the amount of suspended particles and can suggest runoff or poor light penetration. Dissolved oxygen indicates how much oxygen is available for aquatic life and is therefore a key measure of ecological health. Other valid parameters such as pH, conductivity or coliform bacteria could also be discussed if explained correctly.
Q2 (4 marks): Warmer water holds less dissolved oxygen because gas solubility decreases as temperature rises. This means aquatic organisms may have less oxygen available for respiration even if no extra pollutants are added. As a result, fish and other aerobic organisms can experience stress more easily in warm water. The ecological risk becomes even greater if pollution is later added as well.
Q3 (5 marks): Conductivity is useful because it gives a fast indirect indication of dissolved ion concentration and can help track salinity-related issues in a river system. However, conductivity alone is not enough to judge water safety because it does not show which ions are present, whether bacterial contamination exists, or whether dissolved oxygen is sufficient for aquatic life. Other parameters such as pH, dissolved oxygen, turbidity and coliform bacteria must also be considered. Overall, conductivity is an important monitoring tool, but it should be interpreted as part of a broader water-quality dataset rather than as a stand-alone measure of safety.
Scale the platforms using your knowledge of water quality parameters and standards. Pool: lessons 1–6.
Tick when you've finished the activities and checked your answers.