Glossary

• Operation
  refers to the procedures and activities involved in the actual delivery of services, e.g. abstraction, treatment, pumping, transmission and distribution of drinkingwater.
• Acoustic logger
  An electronic device to record levels of noise created by a leak at predetermined time intervals may include correlating acoustic loggers
• Active leakage control
  The process by which unreported leaks are detected and repaired. This contrasts to Passive Leakage Control.
• Average Zone Night Pressure
  The property-weighted average pressure in a zone during the minimum night flow period.
• Awareness Time
  The time between the occurrence of an unreported leak and the water undertaking becoming aware of its existence
• Background leakage
  The component of leakage that is not affected by ALC. This usually consists of very small leaks.
• Cascade
  A method of supplying DMAs where water flows through one DMA into another one. This necessitates more than one meter on some DMAs; a situation that is best avoided.
• Crisis maintenance
  maintenance undertaken only in response to breakdowns and/ or public complaints, leading to poor service level, high O&M costs, faster wear and tear of equipment, and user’s dissatisfaction
• Customer night use
  The water used by customers during the minimum night flow period
• District Meter Area
  A small discrete metered area within the distribution network. The term Distribution monitoring Area is also used to describe the same thing
• Economic Level of Leakage
  The level of leakage at which the net present cost of operation of the network is a minimum.
• Flushing
  The induction of high flows in pipes by opening hydrants or washouts
• Ground Microphone
  A device placed on the ground which amplifies the sound created by a leak to facilitate its location
• Hydraulic Balance Point
  In a complicated network fed by several trunk mains, there will be points within the distribution mains network where the net flow is close to zero at a given time, as flows from different routes feed the customers on either side. These hydraulic balance points are often suitable for sector or DMA boundaries as the closure of a valve here will cause little disruption.
• Infrastructure
  The physical components of the distribution network. This normally excludes electrical components.
• Leakage
  is one of the components of the total water lost in a network, and comprises the physical losses from pipes, joints and fittings, and also from overflowing service reservoirs
• Leakage Control Zone
  Can be a DMA or more often a sub-part of a DMA which is established for the specific purpose of implementing a leak detection exercise
• Leak Detection
  This is the process of ‘narrowing down’ or localization of a leak or leaks to a particular section of a pipe network
• Leak Location
  Is the identification of the position of a leak (pinpointing) prior to excavation and repair. Note: leak location surveys can be undertaken with or without prior leak detection activity.
• Leak Noise Correlator
  An electronic device for matching the sound frequency spectrum from two different locations for the purpose of locating or pinpointing leaks.
• Location Time
  The time taken from the point where the Water Undertaking is aware of the existence of a leak to the point when the undertaking is aware of the exact location of the leak.
• Losses
  Losses can be divided into apparent losses (meter errors and unauthorised consumption) and real losses. Real losses are equivalent to leakage from mains and service connections and overflows from service reservoirs and treatment plants
• Maintenance
  refers to activities aimed at keeping existing capital assets in serviceable condition, e.g. by repairing water distribution pipes, pumps and public taps.
• Management
  Management deals with the control and organization of a service and encompasses the following main functions: • Development of a vision and strategy • Planning • Organization and mobilization of resources • Administration • Accounting • Leadership, motivation of personnel • Supervision, monitoring and evaluation • Promotion of external relationships
• Minimum night flow
  The net flow into a metered area during the period of minimum flow: this period is usually one hour.
• Night Day Factor
  The factor by which night flow losses, (calculated from the Minimum night Flow over a one hour period), should be multiplied to obtain the daily leakage. The NDF is usually less than 24, due to lower pressures during the day
• Passive Leakage Control
  Leakage control carried out by repairing only those leaks that become visible and are reported to the Water Undertaking
• Pressure Reducing Valve
  A control valve within the network which reduces the downstream pressure using various types of control method.
• Pressure Correction Factor
  If leakage (L0) is either measured, or estimated, at one pressure (P0), then in order to estimate the leakage (L1) at another pressure (P1), a relationship of the form: L L .PCF 1 0 = can be used. The PCF is a function of the two pressures P1 and P0. This method is frequently used to translate leakage estimated at 50m head into leakage at the actual pressure experienced in a zone.
• Preventive maintenance
  maintenance activities undertaken in response to prescheduled systematic inspection, repair and replacement, leading to continuity in service level, O&M costs spread over time, extension of life-span of equipment, user’s satisfaction and willingness to pay
• Real Losses
  Physical water losses from the pressurized distribution system, up to the point of measurement of customer use. The volume lost through all types of leaks, bursts and overflows (from service reservoirs or storage tanks) depends upon the frequencies, flow rates, and average duration of individual leak
• Rate of Rise of Leakage
  The rate at which leakage increases with time between periods of active leakage control. This can be measured by analysis of long-term flow and repair records. It is usually expressed in litres per connection per day per year
• Repair Time
  The time taken from the point when the undertaking is aware of the exact location of the leak to the point when the repair is completed
• Reported burst
  A leak that the water undertaking becomes aware of without any detection activity. The reasons for this are typically that the water becomes visible on the surface or the burst leads to loss of supply to customers
• Rota cuts
  Rationing of supply by providing supply to parts of the distribution network for restricted periods, often according to a timed rota.
• Run time of burst
  The total time from the occurrence of a burst to its repair.
• Sector
  A section of the distribution network, usually much larger than a DMA and often defined by clear natural or manmade boundaries, such as rivers or railways.
• Sounding – direct
  A method of locating leaks in which a trained leakage engineer listens to the characteristic sound of a leak by placing a listening device e.g. listening stick or leak noise correlator onto a fitting such as a sluice valve, hydrant or stopcock.
• Sounding – Indirect
  A method of locating a leak but with the listening device in contact with the ground surface e.g. a ground microphone
• Step test
  A test to find the location of a leak. Parts of an area fed through a meter are progressively isolated while the flow is monitored. The drop in flow after each isolation is used to identify the amount of leakage in that isolated section
• Sustainability
  A service is sustainable when: • it functions and is being used • it is able to deliver an appropriate level of benefits (quality, quantity, convenience, comfort, continuity, affordability, efficiency, equity, reliability, health) • it continues over a prolonged period of time (which goes beyond the life-cycle of the equipment) • its management is institutionalized (community management, gender perspective, partnership with local authorities, involvement of formal/ informal private sector) • its operation, maintenance, administrative and replacement costs are covered at local level (through user fees, or alternative financial mechanisms) • it can be operated and maintained at local level with limited but feasible external support (technical assistance, training, monitoring) • it does not affect the environment negatively
• Total water loss
  (Unaccounted-for water UFW) describes the difference between the amount of water produced and the amount which is billed or consumed.
• Unreported burst
  A burst which can be found by active leakage control but not by passive leakage control.
• Water Undertaking
  A general term for the organisation responsible for operation of the water supply and distribution system
• Zero pressure test
  A test to identify whether the boundary to a zone is watertight. An area of the distribution system is isolated by closing boundary valves. The pressure is monitored and if it drops to zero this indicates that the boundary is watertight
• Alum
  Aluminium sulphate (AL2(SO4)3): the most widely used coagulant throughout the world
• Around the end mixing
  A channel where the water passes alternately around the ends of the baffles
• Coagulated water
  Raw water after it has received destabilising chemicals that remove the electric charges from the turbidity particles and allows them to combine together and grow
• Collecting or combining channels
  These channels receive water from a series of basins or pipes and carry it to the next tretment unit or to waste
• Declining rate
  This is achieved with an adjustable plate at the filter clogs and needs washing. This system is most widely used now because of its economy and simplicity
• Deep bed filter
  Single media of coal with a depth of 1-1.3m, effective size of 1,5-3,5 mm and highly uniform (about 1,2 uniformity). Very effective with direct filtration.
• Direct filtration
  Applying water to the filter directly after coagulation with little or no flocculation and no settling. The filter does the work. Very economical approach where feasible.
• Disinfected water
  Filtered water having received a disinfecting chemical, usually chlorine and held in the acid range for a period of 30minutes in a baffled basin to control short-circuiting
• Distribution channels
  These distribute the water from a channel or header to a series of basins or pipes
• False filter bottoms with nozzles
  Plastic nozzles of calculated size and number
• Ferric chloride (FeCl3)
  A coagulant that is effective over a wide range of pH. It produces a heavier floc than alum
• Filter media
  Sand is the most commonly used media in the less developed countries. The depth is usually 60-70 cm and the effective size ranges from 0.6 to 0.8, but both depth and size can vary widely. Dual media, of materials of different specific weight, is used throughout the industrialised countries; It usually consists of a layer of anthracite coal over sand. The combination can take a much higher load-four or more times the old conventional load.
• Filter support
  The filter media is supported by a layer of round stones, the sizes of which vary from approximately 2-3 mm to 25-50mm, with the large stones on the bottom and the small stones on top
• Filtered water
  Settled water that has passed through a porous granulated media at a controlled rate. The media can be sand or coal or a combination of the two
• Flocculated water
  The coagulated water is mixed to provide opportunities for particles to come together and form settleable floc. The mixing energy input is high at the beginning and low at the end of the flocculation process
• Gates
  Openings in channels or basins to allow water to flow in or out.
• Gravity
  Energy applied by means of a difference in elevation
• Gutter
  A channel along the filter side either to distribute settle water over the filter or to receive backwash wastewater to discharge to waste
• Hydraulic flocculation
  Mixing energy applied by gravity in a baffled channel or in a basin
• Impeller mixing
  Pushes water from the centre to the sides of the basin causing non-uniform distribution. Mixing is high at the ends of the paddles and low in the centre at the axis
• Leopold plastic block
  A filter precast and designed for air and designed for air and water back wash
• Lime
  The most commonly used alkali to stabilise water before distribution. Three forms are available: limestone (CaCO3), quicklime (CaO) and hydrated lime (Ca(OH)2). Hydrated lime is the most commonly used form for stabilisation
• Manifold
  A main channel providing equal flow distribution to lateral channels
• Mechanical energy
  Energy provided through mechanically operated equipment
• Mechanical flocculation
  Mixing energy applied by mechanical means
• Over and under mixing
  A baffle with a calculated number and size of perforations to introduce a head loss which serves to distribute water unifromly across the inlet or outlet of a basin
• Perforated baffle
  A baffle with a calculated number and size of perforations to introduce a head loss which serves to distribute water uniformly across the inlet or outlet of a basin.
• Precast corrugated filter bottom
  Can be designed for specific flow rates of water and air and can be fabricated on the construction site
• Propeller mixing
  Power applied in a basin providing an axial flow pattern for good distribution
• Rate control devise
  A constant rate is most commonly used in older treatment plants. The devise maintains the rate constant throughout the filter run. These devises are almost always out of adjustment or completely abandoned.
• Raw water
  Water that comes to the plant inlet from the source - river, lake or reservoir
• Reverse gradation support
  An additional layer on top of the filter support, grading from small to large stones. This type of support is much more resistant to shocks and displacement forces.
• Settled water
  Flocculated water after removal of settleable flocs in appropriate basins
• Slide gate
  A gate with a solid light metal or plastic piece that can slide up or down in the opening to control the flow in or out
• Soda ash (Na2CO3)
  Used for stabilising water for distribution
• Stabilised water
  Disinfected water to which alkali has been added to bring the pH to non-corrosive condition
• Trough
  Structures over the filter bed either for distributing settled water in the filter or to receive backwash wastewater for discharging to the gutter