The absence of free elemental oxygen, the state of not requiring or damage by the absence of free elemental oxygen.

A porous, water-logged sub-surface geological formation. The description is generally restricted to media capable of yielding a substantial supply of water.

A depressed landscape that collects storm-water runoff that infiltrates into the soil below through the root zone, prompting pollutant removal.

A mixture of urine, faeces and flush water along with anal cleansing water (if water is used for cleansing) and/or dry cleansing materials. Black water contains the pathogens of faeces and the nutrients of urine that are diluted in the flush water.

A vegetated area ordinarily situated on gently sloping ground designed to filter out pollutants insoluble in runoff. It is also known as filter strip.

A geographical area defined by topography from where all runoff water drains into a reservoir. Often used as a synonym for watershed and river basin.

The introduction of microorganisms, factory-produced chemicals or wastewater in concentrations that render water unsuitable for most uses.

The transfer of storm-water runoff from one location to another.

A pond that is normally dry except following large-storm events when it temporarily stores storm water to attenuate flows. It may also allow infiltration of storm water into the ground.

The supernatant liquid discharged from a septic tank. The liquid separated out from the septage is also referred as effluent.

The process by which a lake evolves into a bog or marsh and ultimately assumes a completely terrestrial state and disappears. During eutrophication, the lake becomes so rich in nutritive compounds, especially nitrogen and phosphorus, that algae and other microscopic plant life become superabundant.

The process of loss of water to the atmosphere from the earth's surface, evaporation from the capillary fringe of the groundwater table, and the transpiration of groundwater by plants whose roots tap the capillary fringe of the groundwater table.

The settled contents of pit latrines and septic tanks. It differs from sludge produced in municipal wastewater treatment plants. The characteristics of faecal sludge can differ widely from household to household, city to city, and country to country. The physical, chemical and biological qualities of faecal sludge are influenced by the duration of storage, temperature, soil condition, and intrusion of groundwater or surface water in septic tanks or pits, performance of septic tanks, and tank emptying technology and pattern.

Also referred to as bio-filtration, the filtering out of storm-water runoff pollutants conveyed with sediment by trapping them on vegetative species in the soil matrix or on geotextiles.

A temporary rise in water level, including groundwater or overflow of water, onto land not normally covered by water.

An area adjacent to a stream or river that experiences occasional or periodic flooding.

Fluvial flooding occurs when rivers burst their banks as a result of sustained or intense rainfall.

A textile or plastic fabric, usually not permeable, designed to separate different fill materials.

A roof on which plants and vegetation can grow. The vegetated surface provides a degree of retention, attenuation, temperature insulation and treatment of rainwater.

The water retained in the intergranular pores of soils or fissures of rocks below the water table.

The movement of water through openings in sediment and rock. It occurs in the zone of saturation.

The total volume of water generated from washing food, clothes and dishware, as well as from bathing, but not from toilets. It may contain traces of excreta (e.g., from washing diapers) and, therefore, also pathogens. Grey water accounts for approximately 65% of the wastewater produced in households with flush toilets.

A condition where the oxygen content in water or air is reduced, thereby threatening the survival of aerobic organisms.

The continuous cycle of movement of water within the earth. Water evaporates from the earth, condenses in the atmosphere, falls as rain and finally reaches the oceans as rivers, coastal runoff and groundwater flows. The entire process is driven by the energy of the sun.

The entry of rainfall or surface water into the soil.

Aquatic plants growing in or near water. They may either be emergent (i.e., with upright portions above the water surface), submerged, or floating. Examples of macrophytes include cattails, hydrilla, water hyacinth and duckweed.

The process by which water, after infiltration into the soil, moves downward or laterally through openings, fissures or fractures within the rocks in response to gravity or differences in pressure. If there is an impermeable layer of rock below, the water flows laterally and joins the stream flow. When there is no impeding layer, the water percolates into the ground and builds up the groundwater table.

Latrine with one or two pits for collection and decomposition of excreta. The liquid generally infiltrates into the surrounding soil.

Latrine with a rural pan, where small quantities of water are poured from a container by hand, to flush away faeces.

Pluvial flooding occurs when an extremely heavy downpour of rain saturates the urban drainage system and the excess water cannot be absorbed.

The direct capture of storm-water runoff, typically from rooftops, for supplementary water uses onsite.

The excess water that flows after precipitation.

The Ramsar Convention on Wetlands of International Importance especially as Waterfowl Habitat is an international treaty for the conservation and sustainable use of wetlands. It is also known as the Convention on Wetlands. It is named after the city of Ramsar in Iran, where the Convention was signed in 1971. The list of wetlands of international importance included 2,266 Ramsar sites in March 2016 covering over 2.1 million square kilometres.

The type of wildlife habitat found along the banks of a river, stream or any other actively moving source of water such as a spring. Generally, refers only to freshwater or mildly brackish habitats.

The grease, oil and other substances floating on the surface of a septic tank.

The semi-solid matter emptied from septic tanks or similar onsite systems. It has an offensive odour, appearance and high concentration of BOD, COD and TSS etc.

A water-tight single-storied tank in which sewage is retained long enough to permit sedimentation and digestion.

The intersection of land with the water surface. The shoreline shown on charts represents the line of contact between the land and a selected water elevation.

The settled matter in a semi-solid condition.

Water resulting from natural precipitation and/or accumulation. It includes rainwater, groundwater or spring water.

Built up urban areas that are hotter than nearby rural areas. Heat islands can affect communities by increasing summertime peak energy demand, air conditioning costs, air pollution and greenhouse gas emissions, heat-related illness and mortality, and water quality.

Storm water from streets of urban areas and adjacent domestic or commercial properties that carries pollutants of various kinds into the sewer systems and receiving waterbodies.

The upper boundary of a specified catchment area for rainfall that contributes to a given drainage area.

Land inundated or saturated by surface water or groundwater at a frequency and duration sufficient to support (and under normal circumstance does support) vegetation (hydrophytes) typically adapted for life in saturated soil conditions (hydric soils).