Words we use and what they mean

This list is to help you understand how we talk about water in our everyday lives. Some of the words here are scientific, some are commonly used in the water industry, and many are found in the NSW high school syllabus.


A chemical substance with a pH of less than 7, which can corrode, react with or dissolve other materials.


A process where air is mixed through or dissolved in a liquid or substance.


Requiring oxygen.


Unique plant-like organisms that capture energy from the sun to make food.

algal bloom

A large and sudden growth of algae that can be harmful to waterways.


A substance with a pH value of greater than 7.


A chemical used in water treatment called a coagulant. It causes small particles to stick together so they can be more easily removed.


Things that provide comfort or convenience such as toilets, taps and bathrooms.


Able to live without oxygen.


Something that contains no free oxygen.


Living or growing in water.

atmospheric hazard

Hazard event originating in the atmosphere, like storms or tropical cyclones.


A basic unit of matter consisting of a central nucleus surrounded by negatively charged electrons.


Gases that surround a planet, like the air that surrounds Earth.

augmented reality

Computer-generated images, sounds or other data overlayed on a real-world environment that produces an enhanced image that is viewed on a screen.


A substance that can be broken down into harmless products in the environment.


The variety of all living things.


Refers to living matter.

biological oxygen demand (BOD)

A measure of the amount of oxygen used by microorganisms in water when breaking down nutrients such as nitrogen and phosphorus.

biological processes

The processes of a living organism, like turning food into energy.

biological reactor

A wastewater treatment system that uses microorganisms to treat effluent.

biological treatment

Using bacteria and other simple organisms to break down nutrients and organic materials in wastewater.


A major terrestrial vegetation community, like a tropical forest, a temperate grassland or a desert.

biophysical processes

Interconnected processes that form and transform natural environments in a cause-and-effect relationship. For example, erosion, deposition, soil formation, nutrient cycling.


Solid substances formed from the by-products of wastewater treatment. Biosolids can be beneficially used by agriculture or forestry.


The area of the Earth where living things are found.


Wastewater containing faecal matter and other pathogens.


An area of land that collects rainwater as it falls to earth and flows to a common point. Often used to refer to the area of land and waterways that feeds into dams.


A substance made up of specific elements.


A gaseous chemical element.


To remove solid particles from a liquid or solution.


Long-term weather patterns.

climate change

Changes in climate over a long time due to natural and/or human causes.

cloudy water

Water that is not clear.


Chemicals that attract and bind together small particles called floc so they can be more easily removed.


A process causing small particles to bind together and form larger ones ('floc'). This makes them bigger, heavier and easier to remove.


The production of electricity and heat at the same time.


A group of plants, animals or people living together in one place.


A mixture of decomposed plant materials, such as vegetable peelings, leaves and animal waste.


The amount of one substance dissolved in another.


The changing of a gas into a liquid, such as water vapour turning into a liquid.


Protection of resources so they are not degraded, depleted or wasted.


Polluting something by adding a substance or contaminant to it.


Deterioration in metals caused by oxidation or chemical reaction from water, air or acid.


A simple one-celled microorganism or parasite that lives in the intestines of vertebrates, including humans.


A wall or barrier built across a river to hold water.

deepwater ocean outfall

An underwater tunnel or pipe that carries treated wastewater into deep ocean water where it is diluted and dispersed.


The wearing down of the land by the erosive action of water, wind or ice. In chemistry: the breakdown of an organic compound.


The process of removing water from something.


The process of removing salt from ocean water to make drinking water.


A substance used for cleaning. Usually a powder or liquid that is mixed with water to remove dirt.


To release water into a river or the ocean.


A chemical process that kills microorganisms capable of causing infectious disease.


If one substance is soluble in another, then it will dissolve in that substance.

dissolved oxygen

Oxygen that is dissolved in water.

dissolved salts

Inorganic substances, e.g. sodium chloride, that are dissolved in water.

distilled water

Water that has had almost all of its impurities removed.

drinking water

Water intended for human consumption but also has other uses.


A community of organisms interacting with one another within the environment in which they live.


What wastewater becomes after it has been treated at a water resource recovery facility. 

effluent reuse

A process where treated wastewater is recycled for beneficial purposes.


The physical, chemical and biotic surroundings of something.

environmental flow

Water released from dams and reservoirs to maintain the environmental flow of rivers, and the plants and animals that rely on this water. 


The wearing away of the Earth’s surface by wind and water.


Relating to or found in estuaries.


The lower part of a river system where fresh water from coastal catchments mixes with ocean waters.


A form of water pollution caused by an excess of nutrients in the water. Usually leads to excessive growth of algae.  


To convert a liquid into a gas, such as liquid water into water vapour.


The process of converting a liquid into a gas, such as liquid water into water vapour.

faecal coliform bacteria

Bacteria found in the intestines of a mammal. Used to test for faeces in waterways.

fair test

A test where one variable is changed at a time and all the other conditions are kept the same.

ferric chloride

An iron-based chemical used in water and wastewater treatment. Also known as iron (III) chloride.


Natural or chemical materials used to make soil more productive.

field work

An investigation done in the normal environment of the subject of the study, rather than in a laboratory or office.


Devices that remove solid impurities from a liquid or solution passing through them.


A process to remove solid particles from a liquid or solution by passing it through a filter.

first-hand investigation

An investigation based on direct personal observation or experience.


The larger particles formed when smaller particles stick together with the aid of a coagulant during the process of flocculation.


The movement of water in a waterway due to gravity.

flow rate

The amount of water that flows from a water device in a given time.


A type of chemical often used in water supply to reduce tooth decay.

geographical challenges

Issues and problems arising from interactions between people, places and environments that threaten sustainability.

geographical processes

The physical and human forces that work in combination to form and transform the world.


A microorganism (bacteria) that causes stomach and intestinal illness.


Greywater is the wastewater from washing machines, dishwashers, showers, baths and basins.


Small insoluble particles in wastewater such as sand, coffee grounds gravel, glass and food particles.


Water located beneath Earth’s surface filling the spaces between grains of soil or rock.


Something that exposes us to the risk of harm.

hydroelectric power

Electricity made from falling water turning turbine generators.

hydrological cycle

The cycle of water between the Earth and the atmosphere powered by the Sun. Also called the water cycle.

hydrological hazard

Hazard events originating in the hydrosphere from changes to the water cycle, like floods and droughts.


The area where the Earth’s water is found in forms like streams, oceans, ice caps and water vapour.


A predictive statement that can be tested.


Unwanted substances such as sediment or chemicals which may need to be removed from water to protect public health and the environment.

industrial discharge

Waste substances produced or left over during manufacturing that are discharged or released into waterways.


Water that soaks into the ground during and after rain.


A substance not able to be dissolved.

intermittently decanted aerated lagoon (IDAL)

A pond or tank where wastewater undergoes several treatment processes in rotation including sedimentation, biological treatment and clarification.


Supplying water to land to grow plant crops using a system of artificial channels, pipes, sprinklers and/or drippers.


An area created by a combination of geological, geomorphological, biological and cultural layers that have evolved over time.


Earth’s outer rocky shell, including all the rocks and soil that cover the planet.

litter boom

A floating device with a hanging mesh curtain used in creeks and stormwater channels to trap floating rubbish.


An assessment of what a place is like to live in, using criteria such as environmental quality, safety, access to shops and services and cultural activities.


An animal that does not have a backbone and is large enough to be seen with the naked eye.


Thin layers of material that allow only some substances from a solution to pass through them.

methane gas

A simple hydrocarbon without colour or odour produced when microorganisms digest solid waste without oxygen present.


Relating to microbiology or microorganisms.


Organisms that are too small to be seen without a microscope.


A solid substance formed through geological processes that has a specific chemical composition, structure, and physical property.


A group of at least 2 atoms held together by strong chemical bonds.


Observing and keeping a record of something.


An organic chemical compound. Small amounts are commonly used as a water disinfectant instead of chlorine gas.

multi-barrier approach

A process of managing land and testing water in catchments, reservoirs, water pipes, water filtration plants and taps, to protect public health and the environment.

natural hazard

When the forces of nature combine to become destructive and have potential to damage the environment and endanger communities, like bushfires, floods and earthquakes.

natural resources

Resources provided by nature.

natural world

Relates to and includes phenomena in the biological and physical world on and beyond the Earth.


A chemical substance used widely in fertilisers, and contained in human waste from the digestion of proteins. Contains nitrogen which is a plant nutrient.


Nephelometric turbidity units are used to measure the amount of material suspended in water making it cloudy (turbid).


A substance that provides nourishment, food or energy.

organic matter

Material from something that was once living but has now decayed.


Animals, plants and other living things like fungi or algae. An individual animal or plant.


A gas without colour, taste or smell essential to plant and animal life.


Able to cause disease.


People’s assessment of places and environments.


pH is the scale used to measure the acidity or alkalinity of a substance.


A chemical substance used widely in fertilisers and detergents. Contains phosphorus, which is a plant nutrient.


An essential nutrient for plants, animals and humans.


Something that contaminates or degrades the environment making it impure or dirty.


Contaminated with harmful substances.


Any harmful change in the environment due to the release of contaminants.


A tiny opening or space that fluids pass through, like tiny spaces between grains of soil or tiny holes in a polymer membrane


Water that falls from the sky as rain, hail or snow. Also a chemical reaction occurring when 2 solutions react to form a solid (a precipitate), used in all forms of water treatment.


Fresh water that falls as precipitation from clouds.

recycled water

Wastewater (sewage) that has been treated to such a level that it can be reused for non-drinking purposes.


Collecting and processing a resource so that it can be used again.

renewable resource

A resource that is replaced by natural processes at a faster rate than it is used.


A built water storage area like a dam or tank that holds water until it is needed.

reverse osmosis

A process where a solution is forced under pressure through a semi-permeable membrane, separating pure water from dissolved salts.


Rainwater that runs over the Earth’s surface and into waterways rather than being absorbed into the soil.


The presence or amount of salt in water and soil.


Solid materials like plastic removed from wastewater by screens.


Any material that floats to the surface of wastewater during treatment, usually removed in sedimentation tanks.


Materials of different sizes that sink or settle to the bottom of a sediment trap.

sediment trap

A device that captures eroded or disturbed soil, often used at construction sites to protect water quality of a nearby waterway.


Sedimentation is a physical wastewater treatment process used to settle out suspended solids in water under the influence of gravity.

sedimentation tanks

Tanks where the process of sedimentation takes place.


Easily affected by slight changes in environmental conditions.

septic tank

An underground tank used to treat wastewater through bacterial activity.

sewage (wastewater)

The used water that goes down sinks, toilets and drains and into the sewerage system. About 99% of wastewater is water.


Netword of underground pipes used to transport wastewater.


Solid matter that is removed during wastewater treatment. It can be processed into a material called biosolids.

social connectedness

A measure of the number and strength of people’s social relationships with other people in the same place, or in other places via face-to-face connections or electronic methods. The opposite of good social connectedness is social isolation or loneliness.


The ability of a substance to dissolve in another substance.


A substance that has dissolved in a solvent.


The mixture formed when a substance (solute) has dissolved in a solvent.


A substance that is able to dissolve a solute to form a solution.

special distribution

The location and arrangement of particular phenomena or activities across the surface of the Earth.


Stormwater quality improvement devices (SQIDs) include trash racks or constructed wetlands that improve stormwater quality by removing litter, sediment and nutrients.


Rainwater that runs off hard surfaces like roofs and roads and is carried away by stormwater drains flowing into local waterways.


A material composed of specific chemicals.


To continue to live or exist, to stay alive, often by coping with harsh or dangerous conditions.

suspended material

Small and light particles dispersed through water that do not sink to the bottom or float to the top.


The pattern of activities that meet the needs of the present generation without harming the ability of future generations to meet their needs.


Able to continue indefinitely without damaging the environment or depleting a resource.


To do something in a way that will not harm the environment or reduce resources. 


How hot or cold something is as measured by a thermometer.


The process of working out the quality of something.


Detailed description or graphical representation of land surfaces.

total catchment management

Sustainable use and management of land, water, vegetation and other natural resources in a catchment.

trade wastewater

Wastewater contaminated as a result of business activities that may contain pollutants such as suspended solids, grease and other chemicals.


The process in which water vapour is transferred from the leaves of plants into the atmosphere.

trash rack

A metal grill placed across stormwater channels to collect rubbish and other pollution.


To physically or chemically process something.

turbid, turbidity

Water that is cloudy or not clear, caused by suspended materials such as sediments or plankton.


A machine powered by wind, water or steam to produce electricity.


Invisible radiation present in the ultraviolet range of light.

upper catchment

The highest parts of a catchment where a waterway begins.


Relating to a town or city.

urban areas

Areas with a higher population density than surrounding areas such as towns or cities.


The process of economic and social change in which an increasing proportion of the population of a country or region live in urban areas.

urban water cycle

The urban water cycle is the way water is collected, used and managed in an urban environment such as Sydney.


The extent to which the test and results measure what was intended.


Fine particles of a liquid suspended in a gas such as air. Examples are fog, mist or steam. Another word for a gas.


The plant life of an area.


A microorganism that reproduces inside the cells of living hosts.


The used water that goes down toilets, sinks and drains and into the sewerage system. Also known as sewage. About 99% of it is water.

wastewater overflow

This occurs when a wastewater pipe is blocked or flooded by heavy rainfall, resulting in wastewater overflowing into the environment.

wastewater system

The system comprising pipes, pumping stations and water resource recovery facilities used to collect, transport and treat wastewater, then discharge the effluent.

water resource recovery facility

A place where wastewater is treated, including to a high (tertiary) standard so that it can be recycled for a range of beneficial, non-drinking, purposes. 

water cycle

The cycle of water between the Earth and the atmosphere, powered by the Sun. Also called the hydrological cycle.

water cycle processes

The physical changes to water that change its state and geographical location, e.g. evaporation, precipitation.

water filtration plants

A place that filters and treats raw water to make it suitable for drinking.

water scarcity

The lack of sufficient available water resources to meet demand.

water table

The top of a groundwater reserve.


The conditions in the atmosphere like temperature, humidity, cloud cover, rain or wind at a particular place over a short space of time.