Author: Unknown (Anon., 2006)



The quantity that can be contained exactly or the exact rate of flow.

Carbonate alkalinity:

Alkanlinity caused by carbonate ions.

Carbonate hardness:

Hardness caused by the presence of carbonate and bicarbonates of calcium and magnesium.


The area tributary to a stream or lake.


Clearness of liquid as measured by a variety of methods.


A natural occurring material, usually being activated and used as an adsorbent.


Aggregation of microparticles into microfloc, by charge neutralisation.


A substance added to destabilise colloids in a stable suspension.


Finely divided solids, less than 0,001 mm in size, intermediate between a suspension and a true solution.


The top of a dam, dyke, spillway or weir.


Filtration interval, length of time filter operates before cleaning.


A barrier constructed across a water-course for the purpose of creating a reservoir.


Used in conjunction with modifying terms, e.g. biochemical oxygen, chlorine, oxygen, water.

Density current:

A flow of water through a larger body of water, retaining its unmixed identity because of a difference in density.

Depth Filtration:

The use of a deep bed of medium to remove particulate matter by filtration.

Diatomaceous earth:

Diatom skeletons of silica in the form of finely particles, used in cake form as a filter medium.


The rate of flow of water in a stream or conduit at a given place and within a given period of time.


Killing or inactivation of the larger portion of micro organisms, with probability that all pathogenic bacteria can be killed by the agent used.

Earth Dam:

A dam, the main section of which is composed principally of earth, gravel, sand, silt and clay.


The branch of biology dealing with the relationships between organisms and their environment.

Effective storage:

The volume of water available for a designated purpose.


Liquid or waste water flowing out of a resevoir, a sewer or a purification works.


Wearing away of land by running water and by wave action.


The process by which water becomes a vapour at a temperature below boiling point.


Water with drawn from soil by evaporation and plant transpiration.


The mixture of particles and fluid that is deposited on a septum in a diatomaceous earth filter.


A filtration device or a structure consisting of supported filter medium and equipment for the subsequent removal of the deposited solids.


To filter i.e. the operation of passing a liquid through a porous or open textured medium in order to remove suspended particles by leaving them behind in the pores of the filtering medium or at the surface of the filter.

Filter aid:

A material added to improve the effectiveness of filtration.

Filter medium:

The permeable material that separates particles from a fluid passing through it.


Aggregation of micoflocs into flocs by collisions due to hydro-dynamic operation.


Substances added to a destabilised suspension to accelerate flocculation, densify or strengthen flocs.


A relatively high flow as measured by either gauge height or discharge quantity.

Flow rate:

The unit rate at which a product is passed through a system.

Fuller’s earth:

Clay i.e. hydrous aluminum silicate.


The branch of hydrology relating to subsurface or subterranean waters.


The science that deals with the origin, history and structure of the earth, as recorded in the rocks, together with the forces and processes now operating to modify rocks.


Subsurface water occupying the saturation zone from which wells and springs are fed.


A characteristics of water, imparted by salts of calcium, magnesium and iron such as carbonates, bicarbonates, sulfates, chlorides and notates, that causes e.g. curdling of soap and deposition of scale in boilers.


The height of the free surface of fluid above any point in a hydraulic system; a measure of the pressure or force exerted by the fluid.


The branch of engineering science which deals with water or other fluid in motion.


The branch of hydrology that deals with groundwater, its occurrence and movements, its replenishment and depleting, the properties of rocks that control groundwater movement and storage, including for the investigation and use of groundwater.

Hydrologic cycle:

The circuit of water movement from the atmosphere to the earth and return to the atmosphere through various stages or processes such as precipitation, interception, runoff, infiltration, percolation storage, evaporation and transpiration.


The engineering science concerned with the waters of the earth in all their states, including the physical, chemical and physiological reactions of water with the rest of earth and its relation to the life of the earth.


Water accepting – antonym is hydrophobic.

Hydrostatic pressure:

The total force or force per unit area, exerted by a body of water at rest.


The science which deals with rainfall.


Not allowing, or allowing with only great difficulty, the movement of water, impervious.

Impounding reservoir:

A reservoir wherein surface water is retained for a considerable period of time but is released for use at a time when the ordinary flow of the stream is insufficient to satisfy requirements.


The absorption, flow or movement of water into or through the interstices of soil or porous medium.


Substances which are not of basically carbon structures.


A pore or open space in rock or granular material, not occupied by solid matter.


A charged atom, molecule, or radical, the migration of which affects the transport of electricity through an electrolyte or, to some extent through a gas.


Subject to equal pressure from every side; being in isostatic equilibrium.


The stream of water under pressure issuing from an orifice, nozzle, or tube.

Laninar flow:

The flow of a viscous fluid in which particles of the fluid move in parallel layers each of which has a constant velocity but is in motion relative to its neighboring layers; streamline flow.

Langelier index:

The hydrogen ion concentration that a water should have to be in equilibrium with its content of calcium carbonate.


To cause water to percolate through something.


The uncontrolled loss of water from artificial structures as a result of hydrostatic pressure.


Scientific study of fresh water, in lakes, ponds, and streams, with reference to their biological, geographical, physical and other features.


A substance that flows freely, by movement of the constituent molecules, but without the tendency for the molecules to separate from one another.


A tract of soft, wetland, usually vegetated by reeds, grasses and small shrubs.

Mean annual precipitation:

The average over a period of years of the annual amounts of rainfall, MAP.

Mean annual runoff:

The average over a period of years of the annual amounts of runoff discharged by a stream; MAR.


The unit of length equivalent to 10-6m.


Minute organism, either plant or animal, invisible or barely visible to the naked eye.

Milligrams per litre:

A mass / volume unit of concentration of constituents of water or wastewater.


Any substance that is neither animal nor vegetable; obtained by mining.


The sheet of water overflowing a weir or dam.

Normal flow:

The flow that prevails for the greatest portion of time; the mean or average flow.


Chemical substances of animal or vegetable origin, basically carbonaceous.


Precipitation caused by the interference of rising land or air in the path of moisture laden wind.


The addition of oxygen to a compound or a reaction which results in loss of electrons from an atom.

Parts per million:

Milligrams per litre.


The maximum quantity that occurs over a short period of time.


When water, under the force of gravity, passes through soil or rocks, along the line of least resistance.


A stream flowing through all seasons of the year, during wet and dry years.


A material permitting appreciable movement of water through when it is saturated, under normal hydrostatic pressure.


The reciprocal of the logarithm of the hydrogen ion concentration.


The upper boundary of the water table in soil; the phreatic line lies between the capillary zone and the saturation zone.


Having small passages; being permeable to fluids; porosity is the ratio of volume of voids to bulk volume.


The deposition of a filter aid on the surface of a filter or septum before filtration takes place.


The removal of undesirable or objectionable matter from water by natural or contrived means – an extractive process.


The return of clarified liquid for another cycle of phase separation.


A permeable material used to support filter medium.


Liquid above settled solids.


A basin, lake, pond tank or other space which is used for storage; impoundment.


A large stream of water that serves as the natural channel for the drainage of a basin of considerable area.

River basin:

The area drained by a river and its tributaries.


(1) In engineering, a natural aggregate of mineral particles connected together by strong, permanent forces of cohesion.

(2) In geology, the material that forms the essential part of the earth’s solid crust

(3) In groundwater hydrology, all formations in the lithosphere.


A condition reached by a material holding another material in an amount such that no more can be held within it in the same state.


Solids, settled from suspension in a liquid.


The process of deposition of sediment from water.


Neither entirely arid nor strictly humid, but with a tendency towards an arid character.


The spent water of a community wastewater.


Soil particles of diameter 0.004 to 0.062 mm.


Earth material that has been so modified and acted upon by biological, chemical and physical agents that it will support rooted plants.


The impounding of water, either in surface or in underground reservoirs, for future use.


A course of running water, flowing in a definite channel, in a particular direction.


The improvement in performance achieved because two agents are working together.


A measure of the scattering and absorption of light rays, caused by the presence of fine suspended matter.


The fluid property caused by irregular variation in the speed and direction of movement on individual particles or elements of the flow.

Unaccounted for water:

Water taken from a source into a distribution system, but is not delivered to the consumer or otherwise accounted for.

Unit process:

In which chemical changes take place.

Unit operation:

In which physical changes take place.

Water consumption:

The consumptive use of water for any particular purpose.

Water demand:

A schedule of water requirements for domestic, industrial, irrigation, mining and power generation.

Water purification:

The removal of undesirable substances from water.

Water requirement:

The need for water, e.g. for plants, recreation and the environment.


The divide between drainage basins.

Water supply:

In general, the sources of water for public or private uses.

Water treatment:

The addition of substances to water in order to render it more suitable for any particular purpose.

Water works:

As defined under the Water Act, 54 of 1956.


The quantity of water, expressed as a rate of flow, that can be collected for a given use, from surface or groundwater sources on a watershed. Yield would vary with the proposed use, assurance of supply and economic considerations.

Zeta potential:

Directly proportional to electro-phoretic mobility of a particle and a measure of colloid stability.