Water Quality

We rely on your help to protect our waterways. Once a substance other than rain enters the stormwater drainage system, it can cause water pollution and harm local waterways.

Is It Pollution or Iron-Fixing Bacteria?

Sometimes you may notice copper-brown slime on the surface of water in a local creek or waterway. In some cases, this may be naturally occurring iron-fixing, or oxidising, bacteria rather than pollution.

You can use the following simple checks to help determine whether it may be iron-fixing bacteria or a pollution incident:

1. Surface test: Using a stick, poke the water. If the surface shatters like ice, it is likely iron-fixing bacteria. If it clings to the stick and joins back together, it is likely oil from a pollution incident.
2. Smell test: If the water smells like decaying organic matter, it is likely iron-fixing bacteria. If it smells like petrol, sewage or chemicals, it is likely from a pollution incident.

If you are unsure, please log a request with Council below so Council officers can investigate further.

How to Report Water Pollution

Use the following guide to determine who should be contacted in the event of a water pollution incident. 

Penalties for Pollution

Water pollution is prohibited under section 120 of the Protection of the Environment Operations Act 1997.

A person who pollutes, causes or permits waters to be polluted may be committing an offence.

• Serious offences may result in court action, significant fines and possible imprisonment
• Penalty notices, sometimes called on-the-spot fines, may be issued for some offences
• The level of penalty depends on the type of offence, whether the offender is an individual or corporation, and the circumstances of the pollution

Everyone can help protect waterways by making small, simple changes:

Around the Home

• Put leaves and grass clippings in green waste bins - not the street
• Avoid overusing fertilisers
• Keep gutters and drains clear of debris
• Dispose of rubbish properly

Cleaning and Maintenance

• Wash cars on grass or lawns and reduce detergent use
• Clean paint brushes on grass, away from drains
• Reuse or contain water from pressure cleaning
• When pressure cleaning, minimise water-blasting where possible, prevent spray drift, collect solids and residues in sealed containers, and use reliable equipment to avoid leaks
• Never allow pool chemicals to enter stormwater drains
• Check pool acidity and chlorine levels and make sure pool water and chemicals do not enter stormwater drains

Building and Renovation

• Keep soil and building materials away from drains
• Cover stockpiles or use erosion control measures so soil, sand, mulch and other materials are not washed into gutters, drains or waterways
• Mix cement, mortar and concrete in a contained area, such as an old wheelbarrow or bunded area, so excess water, residues and waste cannot enter the stormwater system
• Let concrete slurry dry, then sweep and dispose of it properly
  
  

Tip: Grass clippings are a major pollutant. When washed into drains, they add nutrients such as phosphorus and nitrogen to waterways. This can cause algal blooms and excess weed growth. As the organic matter breaks down, oxygen levels can fall, making it harder for native plants and animals to survive.

Water quality is commonly assessed using the Australian and New Zealand Guidelines for Fresh and Marine Water Quality, previously known as the ANZECC guidelines. These guidelines help water managers assess, manage and monitor fresh and marine water quality.

The guidelines use indicators and trigger values to help identify whether water quality is supporting environmental values such as aquatic ecosystems, recreation and visual amenity. If results are outside the trigger value range, there may be a risk to the waterway and further investigation or action may be required.

Water Sampling Program

Council’s Environmental Health Team is undertaking a water sampling program to assess a range of chemical and biological parameters in local waterways. The Hills Shire includes both urban and rural areas, with a range of potential pollutants that can enter waterways and affect water quality.

Results of the testing program will be updated every quarter.

Waterways Being Tested

Rural locations

• Little Cattai Creek at Wisemans Ferry Road, Cattai
• Cattai Creek, Hidden Valley Road, Glenorie
• Cataract Creek, Maguires Road, Gables
• Blue Gum Creek, Annangrove Park, Annangrove

Urban locations

• Excelsior Creek, Bidjigal Reserve, Castle Hill
• Darling Mills Creek, Richard Webb Reserve, Aiken Road, West Pennant Hills
• Cattai Creek, Fred Caterson Reserve, Castle Hill
• Strangers Creek, Arnold Avenue, Kellyville

Water Quality Parameters

The water samples are assessed against the Australian and New Zealand Guidelines for Fresh and Marine Water Quality. These guidelines support water quality management across Australia and New Zealand.

Electrical conductivity

Electrical conductivity measures the total salts in water. It can indicate changes in the chemical condition of an aquatic ecosystem.

Guideline value: ≤ 500 µS/cm

pH

pH measures how acidic or alkaline water is. The scale ranges from 0 to 14, where 7 is neutral.

Changes in pH can directly affect aquatic life and can also influence the toxicity of other pollutants.

Guideline value: 6.5 – 8.5

Dissolved oxygen

Dissolved oxygen refers to the amount of oxygen in water. It is an important indicator of a waterway’s ability to support aquatic life.

Dissolved oxygen can decrease due to natural events, such as heavy rainfall, or pollution events, such as sewage overflows.

Guideline value: ≥ 6 mg/L

Turbidity

Turbidity describes how clear or cloudy water is. Higher turbidity means there are more suspended particles in the water, making it appear murkier.

Turbid water can reduce the amount of light entering the water and may limit aquatic plant growth.

Guideline value: < 5 FAU

Nitrate, total phosphorus and total nitrogen

Nitrogen and phosphorus are essential for aquatic life. However, excessive concentrations can promote nuisance plant growth and cause eutrophication, also known as nutrient pollution.

Elevated nitrogen and phosphorus can result from natural sources and human activities, including cleared land, fertiliser run-off and sewage discharges.

Total nitrogen and total phosphorus measure all forms of nitrogen or phosphorus in a sample. Nitrate is an inorganic form of nitrogen that is available for plant growth.

• Nitrate guideline value: ≤ 0.3 mg/L
• Total phosphorus guideline value: ≤ 0.05 mg/L
• Total nitrogen guideline value: ≤ 1.0 mg/L

Enterococci

Enterococci are bacteria found in the intestinal tracts of humans and animals and are commonly associated with sewage contamination. Some areas of The Hills Shire are not connected to Sydney Water’s wastewater system and rely on onsite sewage management systems, which often use land disposal.

If these systems are not maintained, they can pose a risk to waterways.

While no criteria have been adopted for enterococci, samples are being collected and analysed by Sydney Water. The results will be used to identify areas where further investigation may be needed, including targeted inspections of onsite sewage management systems.

Water Sampling Results

Water Sampling - Urban and Rural Test Results - March-May 2026(XLSX, 14KB)