What is Groundwater?

Groundwater is the water which flows underground through spaces between rocks, known as aquifers. Water enters the ground as part of the water cycle (pictured below), when rain seeps into the ground. Due to drought, the use of ground water has more recently become a topic of interest.

Water Cycle – (source: C.S.I.R.O, 2004)

Aquifer Materials

Aquifers are a geological formation which can store and transmit groundwater. They are typically formed of gravel, sand, sandstone, or fractured rock, like limestone saturated with water. These materials are permeable because they have large connected spaces that allow water to flow through. Water in aquifers may be brought to the surface naturally via a spring or discharge into a local creek, river or harbour via the water table.

Groundwater can be found almost everywhere but the depth of the water table may vary. During heavy rain the water table may rise and during extended dry weather may fall. The speed at which the groundwater flows will depend on the size of the spaces in the soil, sand or rocks and how well the spaces are connected. Groundwater supplies are replenished, or recharged, by rain.

It is important to remember that aquifers not only store water, but also act as underground transportation systems to carry the water down the catchment. If the aquifer becomes polluted at some point then the polluted groundwater will be transported to a surface water body such as the creek, harbour or river or a well or bore used for domestic or industrial purposes.

The Importance of Groundwater

The total volume of water on planet earth has remained the same for millions of years. Of all the water on earth, the oceans contain more than 97%, approximately 2.5% is fresh water and the relatively small volume of water remaining is contained in saline lakes.

Of the earth's fresh water, approximately 76% is located in ice caps and glaciers, 23.5% occurs as groundwater and 0.5% is water found in rivers, lakes and reservoirs, as water vapour in the atmosphere and as water stored in animals, plants and in the soil.

Less than 1% of global fresh water is available for human use and, of this 1%, over 97% of the available fresh water resources are found as groundwater.

Groundwater is an important resource in the Sydney Region. It provides continued existence to various economic and social activities in the region as well as being essential for the preservation of local waterways, estuarine and wetland ecosystems which provide valuable natural habitats for flora and fauna. In some instances groundwater may also be used for domestic and commercial uses. All users of groundwater in NSW require a licence from the Office of Environment and Heritage.

Using Groundwater in Willoughby

Groundwater in the Northern region of Sydney is not considered suitable as an alternate resource for non-potable purposes. The aquifer is very deep (approximately 120 metres below ground level) and therefore expensive to access. The aquifer lies below ironstone and shale layers which generally leach salt making the groundwater unsuitable for irrigation without further treatment.

Groundwater and development

Large-scale development such as multi-storey buildings or smaller unit sites with underground carparks may interfere with the existing water table or groundwater course. It is common practice in these situations for the groundwater to be collected by a sub-soil drainage system that is then pumped to the nearest street kerb or street stormwater system.

This method of discharge may become a nuisance to the surrounding community and/or to traffic and pedestrians as well as being a loss of a valuable natural resource.

The water has to go somewhere

Developers in these circumstances should look at possible alternative methods of disposal or reuse of the groundwater. However there are other concerns which must be considered by the developer such as:

(a) will lowering the level of the groundwater lead to any compaction of the foundation materials supporting existing buildings and structures potentially resulting in structural damage?
(b) can the community afford the loss of a groundwater resource?

Information with regards to groundwater management, both during and after construction of a development site, needs to be included in a Water Management Plan when submitting a Development Application to Council.

Remember, all users of groundwater in NSW require a licence from the Office of Environment and Heritage.

Groundwater Contamination

In areas where the land material above the aquifer is permeable, pollutants can sink into the soil, sand or enter through cracks in rocks and find its way into the groundwater. If the groundwater becomes polluted, it will become unsafe or unfit for such purposes as drinking, irrigation, and reuse for other domestic and commercial purposes or to flow into the local creeks, river or harbour.

Contamination of groundwater may be an existing problem in some older urbanised areas and, where there is increasing urbanisation, from both point source and diffuse contamination sources.

Point source contamination:

  • Leakage from aboveground and underground storage tanks which may contain petrol, oil, chemicals, or other types of liquids and develop leaks due to corrosion and cracking.
  • Leakage from underground services such as septic tanks and sewer pipes designed to drain human waste. An improperly designed, located, constructed, or maintained septic tank can leak bacteria, viruses, household chemicals, and other contaminants into the groundwater. Likewise, cracks or leaking joints in sewer pipes may release the same contaminants.
  • Spillage of chemicals from barrels or other containers lying around industrial or building sites that are full of hazardous materials could lead to groundwater contamination if there is a leak, they are improperly stored or mishandled.
  • Leachate from former garbage tips where there is no protective bottom layer to prevent contaminants such as car battery acid, paint, household cleaners, etc. from getting into the groundwater.

Diffuse contamination:

  • Overuse of garden fertilizers and pesticides can move through the soil and find their way into the groundwater from the surface over time due to either prolonged and/or heavy use.
  • Some of the same pollutants that contaminate surface water may contaminate groundwater such as contaminated runoff from roads, commercial and industrial areas.
  • Airborne pollutants such as lead from motor vehicles.

Dangers of Contaminated Groundwater

Drinking contaminated groundwater can have serious health effects. It is important to note that local flora and fauna may be relying on, and can also be harmed by, contaminated groundwater.

Diseases such as hepatitis, cholera, typhoid and dysentery may be caused by contamination from septic tanks or sewage leaks. Poisoning may occur due to toxins leaching into the groundwater or nutrient levels may increase (primarily from phosphorus) which promotes algae and weed growth in our creeks and the river and depletes oxygen levels resulting in fish kills.

What you can do to prevent Groundwater Contamination

Once groundwater becomes polluted, it is difficult to clean up completely. The cost of cleaning up groundwater systems is very high, if at all possible. It is far better to prevent or reduce the risk of groundwater contamination than to deal with its consequences.

  1. Report any incidents of pollution or dumping that you may see to your local Council.
  2. Adopt pollution prevention and conservation practices in order to protect groundwater supplies.
  3. Minimise potential impacts of on-site wastewater treatment systems through: regular inspections, not overloading the wastewater treatment system by minimising the amount of water entering the system using water conservation practices, not planting trees or shrubs with deep penetrating roots or drive or park heavy vehicles and equipment near the drainfield, limit the types and amounts of wastes poured down the drain.
  4. Use fewer toxic raw materials, less fertiliser and switch to phosphate-free detergents. You can view a table listing  Potentially harmful components of common household products.
  5. Prevent the salts contained in Australian soils from rising to the ground surface by retaining large trees or planting more trees.


Water Quality

Dissolved solids present in groundwater can cause problems. For example a high level of calcium and magnesium carbonates causes the water to become "hard" and hard water causes scaly deposits to form in water heaters and pipes, and makes soap difficult to lather. Also, sulphates in water can leave a bitter taste, and can also have a laxative effect. You can view a table outlining some  Common chemicals and their effect on water quality.

More information and helpful links

For additional technical and regulatory information please refer to Sydney Coastal Council’s website for their Groundwater Factsheets and Groundwater Management Handbook.

Office of Environment and Heritage also has a helpful website.


1. The Groundwater Foundation
2. The Macmillan Dictionary of the Australian Environment
3. The Parliament of the Commonwealth of Australia - The Value of Water: Inquiry into Australia’s management of urban water

Some material was reproduced from with the permission of The Groundwater Foundation. Copyright ©2002, The Groundwater Foundation. All Rights Reserved. Some material was reproduced from with the permission of “, Watertable Watch Programme” and attributed to the Victorian Salinity Program - Watertable Watch programme circa around 1991-2.