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| Absorb | To physically or chemically assimilate a substance and include it in another; to take up gases, water, nutrients or other substances e.g. by soils or plants. |
| Absorption trench | The disposal field of a conventional domestic on-site effluent disposal system; an excavated area, filled with gravel with a light cover of soil from which water from a perforated pipe from a septic tank can evaporate and percolate into the surrounding soil. |
| Acid | A substance containing more H+ ions than OH- ions in solution; a condition where the pH is below 7, where the activity of the H+ ion exceeds that of hydroxyl OH- ions. |
| Activated carbon | High porosity, high surface area carbon obtained by burning organic matter in the absence of air, which possess a high capacity to remove trace and soluble components from solution; used to remove impurities causing odour and undesirable taste from drinking water by absorbing gases and various organic and inorganic molecules. Also used for removing cyanobacterial toxins from drinking water. |
| Activated sludge | A rich mixture of bacteria and mineral substances that has been through a reactor tank and which is to be reintroduced, aerated and mixed with the incoming sewage; a type of sewage treatment plant in which the above process is used to break down organic matter and nitrogen compounds. |
| Acute poison | A toxin that quickly causes a crisis situation to be reached; not chronic |
| Adsorb | Attach a substance to the surface of a liquid or solid e.g. cations to a negatively charged clay or other colloidal material; retain water, ions or exchangeable bases on a colloidal surface. |
| AEAM | Adaptive Environmental Assessment and Management |
| Aeration | Exposure of a material to air so that dissolved gases may be removed; the process by which air is added to a substance or exchanged with an existing atmosphere. |
| Aerobic | Adapted to the presence of oxygen; growing or occurring only in the presence of molecularoxygen; having molecular oxygen as part of the environment; bacteria that require oxygen in order to survive and multiply. |
| Aerobic digestion | Breakdown of organic matter in a liquid medium in the presence of oxygen or air. |
| Aerosol | A colloidal system of solid or liquid particles dispersed in a gas; very fine particles in the atmosphere e.g. smoke, fog, smog. |
| Aging | The progressive breakdown of organic materials through the cumulative effects of irreversible physiochemical processes over a period of time; nutrient and sediment build up in water storages over time. |
| Algae | Simple photosynthetic aquatic or moist habitat plants, semicellular or in colonies or filaments,some free-floating or having motile cells with flagella, others attached to various substrates or having symbiotic relationship with plants or animals. |
| Algal bloom | A rapid increase in the mass of one or more algae or cyanobacteria (blue-green algae) in a water body, usually in response to a change in its flow, light, temperature or nutrient status. |
| Alkaline | Containing or releasing an excess of hydroxyl (OH-) ions over hydrogen (H+) ions; capacity to reduce or neutralise acidity; a soil or solution with a pH>7. |
| Allocation | The announced percentage of water entitlement that can be used in a particular season. This is normally known as seasonal water allocation and is computed based on available in-storage volume plus 1/100 year inflows. |
| Alum | Hydrated double salt of aluminium and potassium sulphates; a general term used for aluminium sulphate, used as a coagulant in water treatment; the reaction product of sulphuric acid and alumina or bauxite. |
| Ammonia | A colourless alkaline gas NH3, produced synthetically in a modified Haber process from nitrogen in air and hydrogen from methane (natural gas) using catalysts at high temperature and pressure. |
| Anaerobic | Lacking air or molecular oxygen; living or functioning in the absence of air or free oxygen; capable of survival only in the absence of oxygen; bacteria living in such conditions |
| Anaerobic digestion | Decomposition of oxygenic materials under conditions of low air or oxygen supply. |
| Anoxic | Lacking dissolved oxygen; a condition in which oxygen is deficient or absent or exists only in a combined form |
| Antecedent storage condition | The level of water within a wetland prior to the onset of the next inflow event |
| Anthropogenic | Produced or caused by humans |
| Aquatic macrophyte | A large plant capable of living in water or periodically inundated habitats |
| Aquifer | A layer of porous rock that both stores water and allows it to percolate through; underground rocks, gravels or coarse sediments capable of storing water, which may be recovered for irrigation or other consumptive uses. |
| Aquifer recharge | Build up of the water level in a natural underground storage |
| Aquifer storage and recovery (ASR) | The storage of water through wells installed into aquifers, with subsequent retrieval from the same wells during demand for the stored water |
| Artificial wetland | A constructed habitat with either static or running water and aquatic or terrestrial vegetation, with the objective of directly reducing contaminants in the water or creating conditions for this to occur. |
| Australian Drinking Water Guidelines | Portion of the National Water Quality Management Strategy (1996) dealing with the physical, chemical and biological components of water for human consumption. |
| Average Dry Weather Flow (ADWF) | The amount of water moving downstream in a catchment during the dry season; the average daily volume of wastewater entering a sewage treatment plant in dry weather. |
