arrow_backEmergency WASH




Removal of water from a source.


Higher concentration of positive hydrogen ions in the solution, resulting in a low pH value (below pH 7).


The tendency of molecules of liquids or gases clinging to the surface of a solid particle.


Adhesion of a thin film of liquid, vapour or dissolved ions to a solid substance without involving a chemical reaction.


Capacity of water to resist or neutralise acids to maintain a fairly stable pH level.


Loose unconsolidated material (i.e., particles are not cemented together) that was previously deposited by ice or flowing water.


Geological formation capable of storing, transmitting (flow rate) and yielding exploitable quantities of water.

Artesian Aquifer

See Confined Aquifer.



Filling a hole using some of the material that was removed during the digging or drilling process.


Reversal of the flow of water to free a clogging material (e.g., sediments within a rapid sand filter or reverse osmosis filtration cartridges).


Lower concentration of positive hydrogen ions in the solution, resulting in a high pH value (above pH 7).

Biological Contaminants

Organisms in water also referred to as microbes or microbiological contaminants (e.g. bacteria, viruses, protozoa). (Syn.: Microbial/Microbiological Contaminants)

Bone Char

Porous granular substance used for water filtration and decolouration; produced by charring animal bones.


A narrow shaft bored or drilled from the surface to underground water sources for the extraction of water.

Brackish Water

Water with more salinity than fresh water but less than seawater (1,000-10,000 mg/L total dissolved solids). It is usually the result of seawater intrusion into groundwater bodies along coastal areas.


Water with high salinity (e.g. from aqueous sodium chloride used in electro-chlorination systems).


Upward force exerted by water or fluids on objects that are wholly or partly immersed.


Canzee Pump

An inexpensive direct-action hand pump that consists of two PVC pipes inside of each other, each with a simple nonreturn valve made with a rubber flap. Maximal water lifting capacity is 12–15 metres.

Capital Costs

Costs related to the acquisition of a fixed asset or hardware.

Case Fatality Rate (CFR)

A measure of the severity of a disease as defined by the proportion of deaths from a specified disease compared to the total number of people diagnosed with the disease within a specified period of time.


A surface area that collects and drains rainwater and snow melt to a certain point (e.g. a small-scale roof catchment drains water that falls on the roof or a large-scale ground catchment drains water from surrounding land).

Check Valve

A valve that allows liquids or gas to flow through it only in one direction. Also known as a non-return valve.

Chemical Contaminants

Elements or compounds in water that may be naturally occurring (e.g. fluoride, arsenic, nitrate, toxins produced by bacteria) or man-made (e.g. pesticides, heavy metals).

Chemical Oxygen Demand (COD)

Measure of the amount of oxygen required for the chemical oxidation of organic material in water by a strong chemical oxidant (expressed in mg/L). COD is an indirect measure of the amount of organic material present in water – the higher the organic content, the higher the oxygen requirement.

Chlorine Demand

The amount of chlorine added to water that is completely exhausted in the water disinfection process.


Process in which a chemical (e.g. aluminium sulphate or ferric chloride) is added to water to destabilise electrostatic charges of colloids, allowing these smaller particles to come together to form larger particles (through flocculation), which settle out faster or can be filtered due to their larger size.

Coliform Bacteria

Organism found in the digestive tracts and faeces of animals and humans that, when found in drinking water, may indicate the presence of pathogenic bacteria.


Stable insoluble substances that are so small that the random motion of water molecules is sufficient to prevent them settling under gravity.

Commodity Valve

Low priced, widely available, manufactured valves used in water pumping and distribution networks.

Confined Aquifer

A saturated geological formation in which the water pressure at any point is greater than atmospheric pressure. (Syn.: Artesian Aquifer)


Physical, chemical, biological or radiological substance present in water that may be naturally occurring or man-made and that may affect public health if present in levels above water safety standards.



The process of removing salts and minerals from water.


The process of removing silt or deposits from a tank or reservoir.


The process of removing water (e.g. pumping water from an excavation).

Diffused Sources of Contamination

Contamination coming from unspecific pollution sources over a wide area (e.g. pollution from agriculture).


The volume of water that passes a given point within a given period of time. It is an all-inclusive outflow term describing a variety of flows, such as from pipes or streams.


The elimination of pathogenic microorganisms by inactivation (e.g. using chemical agents, radiation or heat) or by physical separation processes (e.g. membranes).

Disinfection By-Products

Chemical, organic and inorganic substances that result from a reaction of a disinfectant (e.g. chlorine) with naturally occurring organic matter in water and that may be harmful.


Further away from the source; the direction in which water is naturally flowing.

Duty Pump

The pump in use most of the time (i.e., not the standby pump).



Outflow of water or another liquid from a pipe or treatment plant that is discharged to a stream or body of water.


A technique using a direct electrical current to drive an otherwise nonspontaneous chemical reaction.


A mound of earth or stone built to hold back water.


The process by which soil and rock are worn way, loosened or dissolved and moved by natural forces such as rain, snow or wind.


The process by which water turns from its liquid phase into gas (vapour).


The process by which water is transferred from the land to the atmosphere by evaporation from the soil and other surfaces and by transpiration from plants.


First Flush

The initial and often sediment- and contaminant-laden surface runoff in rainwater harvesting systems that is diverted away from the storage tank.


Clarifying agents used in water treatment to remove suspended solids from liquids by inducing flocculation.


A physical process wherein particles come together to form larger particles (flocs) following the introduction of floc-creating agents (flocculants) and slow agitation of the water.


Flow rate per area of membrane.


A mechanical device designed to efficiently store rotational kinetic energy, giving mechanical advantage to lifting water.

Friction Loss

Reduction in energy that occurs when water moves due to water molecules knocking into each other and against the pipe wall, which converts some of the total available energy into heat that dissipates into the environment. (Syn.: Head Loss)



A machine that uses fuel (e.g. diesel) to convert mechanical energy into electricity.


The force that attracts an object or substance towards the centre of the earth or towards any other physical body having mass.


Water generated from showers, bathtubs, washing clothes, handwashing and sinks.


Water that is held in pores and spaces within the geological formations of the earth's surface.

Groundwater Recharge

Process wherein groundwater is replenished. To be sustainable, this should be equal to or greater than what is abstracted.

Groundwater Table

The surface of the saturated water-bearing layer in the ground that is open to atmospheric pressure and that is not static but can vary over time due to lower recharge or higher usage.


Head Loss

See Friction Loss (Syn.)


A wall of masonry or concrete built at the outlet of a pipe that functions to support the sides of an excavation as well as (together with the apron) to prevent erosion by water flow.

Heavy Metals

Metals with relatively high density that can enter water supply systems either through artificial sources (e.g. industrial or consumer waste) or natural sources (e.g. released from soils) and that can pose potential health risks.

Helical Rotor Pump

A positive displacement pump that works through the rotation of a helical rotor, which is shaped as a single helix that sits within a stationary double-helix rubber stator. Water occupies the cavity between the two, and when the rotor turns, this cavity moves upwards together with the water. (Syn.: Progressive Cavity Pump)

Hydraulic Cleaning

A set of techniques to clean pipes and sewer lines that includes the use of high-pressure and high-velocity water.

Hydraulic Conductivity

A property of soils and rocks that describes the ease with which a fluid (in this case water) can move through pore spaces or fractures.

Hydraulic Gradient

A measure of the decrease in total energy per unit length in the direction of flow when water is moving, which results from the phenomenon known as head loss.

Hydraulic/Pneumatic Power

Transmission of power by the controlled circulation of pressurised fluid to a motor that converts it into a mechanical output. For pneumatic power, pressurised gas is used.

Hydrogeological Survey

An investigation of geology, groundwater, geochemistry and contamination at a particular site, as well as climatic and recharge conditions, with a view to understanding the risk to groundwater or the usefulness for groundwater supply in a sustainable manner.



A rotating component of a centrifugal pump that accelerates the fluid outwards from the centre of rotation.

Impulse pump

A pump using pressure created by air that pushes part of the liquid upwards.

In Situ

On site or in position.

Industrial Effluent

By-product of industrial or commercial activities, often with high physical and chemical contamination.


Process by which water on the ground surface enters into the soil.


Flow of water into a specific technology.


A part of a machine or structure through which liquid or gas enters.


Material derived from non-living sources (such as rock or minerals) and that does not contain carbon.


An opening through which fluid enters an enclosure (e.g. river intake) or a machine (e.g. pump intake, same as pump inlet).

Integrated Water Resources Management (IWRM)

A process that promotes the co-ordinated development and management of water, land and related resources to maximise the resultant economic and social welfare in an equitable manner without compromising the sustainability of vital ecosystems.

Ion Exchange

Process by which an ion in a mineral lattice is replaced by an ion from a contacting solution.


Jar Test

A laboratory procedure that simulates a chemical treatment process on smaller quantities of water using differing chemical doses.


Kinetic Energy

Form of energy that an object has due to its motion.


Log Removal Values (LRM)

A logarithmic measure of the ability of a treatment process to remove pathogenic microorganisms. An LRM of 1 corresponds to a reduction of 90 %, an LRM of 2 corresponds to a reduction of 99 %, etc.


Managed Aquifer Recharge (MAR)

The intentional recharge of water to suitable aquifers for subsequent recovery or to achieve environmental benefits, with added effects of reducing poverty, reducing risk and vulnerability and increasing agricultural yields.


A thin, pliable sheet or layer of natural or synthetic (filter) material.

Membrane Fouling

Material retained on the surface of the membrane or within the pores that reduces the flow through the membrane.


A pollutant, usually from an artificial source, that is present in extremely low concentrations (e.g. trace organic compounds), yet above background levels.

Microbial/Microbiological Contaminants

See Biological Contaminants (Syn.)


The process or result of making something less severe, dangerous or damaging.


Nephelometric Turbidity Units (NTU)

Measure of how much light shone through a water sample reaches a detector on the other side of the sample. Particles in the water reflect more light sideways, meaning more light arrives at the detector. A higher turbidity results in a higher reading.


Operation and Maintenance (O & M)

Routine or periodic tasks required to keep a process or system functioning according to performance requirements and to prevent delays, repairs or downtime.

Operational Costs

The expenses associated with the operation, maintenance and administration of a specific technology or system.


Material containing carbon-based compounds coming from the remains of organisms such as plants and animals (and their waste products).


Flow of water coming out of a specific technology.


A part of a machine or structure through which liquid or gas exits.


The loss of electrons during a reaction by a molecule, atom or ion, e.g. when iron reacts with oxygen, it forms rust because it has been oxidised (the iron has lost electrons) while the oxygen has been reduced (the oxygen has gained electrons).



A disease-causing organism.


The soil's hydraulic conductivity after the effect of fluid viscosity and density are removed (i.e., describes the innate properties of the soils and rocks themselves).


To diffuse through; to pass through the pores or interstices of something.

Personal Protective Equipment (PPE)

Protective equipment (e.g. clothing, helmets, goggles) designed to protect the wearer from injury or infection.


Stands for power of hydrogen; a scale used to specify how acidic or basic (alkaline) a waterbased solution is. A pH value below 7 indicates that a solution is acidic, and a pH value above 7 indicates that it is basic (alkaline).


The moving component of reciprocating pumps (among others) that is tightly contained within a cylinder.

Point of Collection/Abstraction

Location where water is collected by users (e.g. borehole, tapstand, river or lake).

Point of Use (POU)

Location where the water is actually used and consumed (usually directly at household level).

Point Source of Contamination

Contamination coming from a specific pollution source that can be pinpointed.


Ratio of the volume of interstices (intervening spaces) in a given sample of a porous medium to the gross volume of the sample, inclusive of voids.

Positive Displacement Pump

A pump that displaces a fixed amount of water per cycle.


Condensation of atmospheric water vapour that returns to the earth's surface as e.g. rain, snow, hail or fog.

Progressive Cavity Pump

See Helical Rotor Pump (Syn.)

Protected Spring

A spring that is modified to collect, transport and sometimes store spring water while preventing contamination.

Pump Discharge

The water coming out of a pump or the outlet port of a pump.

Pumping Test

A field test in which the performance of an aquifer is measured through the action of pumping a well to demonstrate well efficiency, possible yield and pump placement.



Water from liquid precipitation.


Refers to water entering an underground aquifer through faults, fractures or direct absorption.


Process when something that had been cleaned again becomes contaminated (e.g. water that is treated gets contaminated again).


The restoration of something damaged or deteriorated to a prior good condition.


An impoundment of surface water in a natural depression that has been enhanced to hold the water by a man-made structure on one or more sides.

Residual Chlorine

The amount of active chlorine remaining in the water after a certain period of time (i.e., 30 minutes of contact time) after the initial chlorine demand has been met.

Residual Pressure

The extra pressure above a tap or outlet that is equal to either the static head (when no water flows) or to a point on the hydraulic gradient (when water flows).


The renewed suspension of a precipitated sediment (e.g. when stirring up mud that has settled at the bottom of a tank).

Rising Main

A pipe from a submerged part of a pump that rises to where water is delivered (e.g. pump head for a handpump or water tank for a submersible pump).


The bed or channel through which water flows, which is located at a lower point in a drainage system.


Water from precipitation that runs off the ground surface (rather than infiltrating), which then enters rivers, lakes or reservoirs.

Run-Off Coefficient

The percentage of water that runs off a surface and can be collected, wherein the remainder is lost (e.g. to splashing, evaporation or infiltration).


Saline/Salty Water

Water that has a high content of dissolved solids and is generally considered unsuitable for human consumption.


The quality or degree of dissolved salt content.

Saltwater Intrusion

The movement of saline water into fresh-water aquifers that can degrade groundwater quality (see also Brackish Water).

Sand Trap

A plain section of casing under the screens at the bottom of a borehole that allows fine silt/sand particles to accumulate during the well development process and over time.


When all the pores of a material or medium (e.g. soil) are filled with water.


The most biologically active part of a slow sand filter, consisting of a dense population of microorganisms that develops over time and that is key to the disinfection properties of the filter.


A device used to prevent objects or particles from entering the water supply. Common examples of screens used in water supply operations include slotted pipes in boreholes or a set of bars used in raw water intakes (Syn.: Well Screen).


The settling out of particles in a liquid by force of gravity.


The slow escape of liquid (e.g. water from a diffuse spring).

Shock Chlorination

A process in which a large amount of chlorine is added to the water to adequately disinfect it, including all the solid particles in the water that would normally increase chlorine demand. After shock chlorination, the water is not safe to drink due to high chlorine levels and must be decanted.

Silt Trap

A device to prevent silt from entering a tank or water treatment system.


The deposition of fine sediment in the bottom of a stream, lake or reservoir.

Skid-Mounted System

A set of equipment that is mounted in a frame(s) to ensure easy and secure transport and usage as a unit.


Process by which a substance is made (more) soluble in water.


A device with holes or made of crossed wires that is used to separate solid matter from a liquid – for surface water pumps, it is used at the end of the inlet pipe to prevent larger materials from entering the pipe.

Submersible Pump

A pump that is located underwater, from where it pushes water. It has a hermetically-sealed motor that is close-coupled to the pump body.

Suction Pump

A pump that is located above the water surface, from where it pulls water by suction into the pump housing.

Surface Water

Water that remains on the ground surface in large bodies (e.g. streams, lakes, wetlands) and that has not infiltrated into the ground.

Suspended Solids

Small solid particles that remain in suspension with water either as colloids or due to the motion of the water.

Sweet Water

Any naturally occurring water with less than 500 mg/L of dissolved salts.


A tube used to convey liquid against gravity upwards from a reservoir and then down to a lower level of its own accord.



The bulk transport of water using a water tanker vehicle, which takes water from the source to a storage facility near a distribution point.

Tara Pump

A low cost and robust direct action hand pump with a buoyant pump rod that displaces water on both the up and down strokes. Maximal water lifting capacity is 15 metres.


The shape and features of land surfaces.

Totally Dissolved Solids (TDS)

The quantity of minerals (salts) in solution in water, usually expressed in milligrams per litre (mg/L) or parts per million (ppm).


The measure of relative clarity of a liquid, usually expressed in Nephelometric Turbidity Units (NTU).


A machine for producing continuous power in which a wheel or rotor, typically fitted with vanes, is made to revolve by a fast-moving flow of water, steam, gas, air or other fluid.


Ultraviolet (UV)

Type of electromagnetic radiation that disinfects through the inactivation of pathogenic microorganisms.

Unconfined Aquifer

A saturated geological formation that is open to atmospheric pressure; its surface is known as the groundwater table.


A concealed drainage area/trench that allows water to pass while retaining material on top (e.g. a drainage area at the bottom of a rapid sand filter).

Unprotected Spring

A spring that is in its natural state and has not been modified to prevent contamination.

Upflow Filtration

Filtration process in which water flows from bottom to top.


Nearer to the source; against the direction in which water is naturally flowing.



Speed, or how far something travels over time.


Water Column

Conceptual column describing the vertical expanse of water between the surface and the bottom of a particular water body.

Water Hardness

A water quality parameter that indicates the amount of dissolved minerals, especially calcium and magnesium. Hard water has higher levels of these minerals.

Water Metering

The practice of measuring the amount/volume of water used.

Water Tariff

The price assigned to water supplied by a public utility (usually through a piped network) to its customers.


Any artificial excavation constructed for the purposes of exploring and extracting groundwater or for injection, monitoring or dewatering purposes.

Well Efficiency

The ratio of aquifer loss (theoretical drawdown) to the total measured drawdown in a borehole/well, which shows the efficiency of the well as an engineering structure for water abstraction.

Well Screen

See Screen (Syn.)



The amount of water that can be abstracted over time.