Water Distribution Operator Class III key terms

A line representing the total energy head of water at each point in a system, plotted as the height water would rise in an open piezometer tube. It falls in the direction of flow due to friction losses.

The reduction in water pressure or energy caused by friction as water moves through pipes, fittings, and valves. It increases with flow velocity, pipe roughness, and length of pipe.

A widely used formula for estimating friction head loss in pressurized water mains based on flow rate, pipe diameter, pipe length, and a roughness coefficient. It applies to full-flowing pipes under turbulent conditions.

A roughness coefficient used in the Hazen-Williams equation that describes the interior smoothness of a pipe. Higher values indicate smoother pipe and less friction loss; older, tuberculated mains have lower values.

The buildup of corrosion products, usually iron oxide nodules, on the inside wall of unlined metal pipe. It narrows the flow area, raises friction loss, and can degrade water quality and pressure.

A defined area of a distribution system served at a controlled range of pressures, usually by a pressure-reducing valve, booster pump, or dedicated tank. Zones prevent excessive or inadequate pressure at customers' taps.

A pipe segment that terminates without connecting to another main, so water cannot flow through it. Dead ends promote stagnation, loss of disinfectant residual, and sediment buildup, and usually require flushing.

Design practice of connecting mains into circuits rather than dead-ending them, allowing water to reach any point by more than one path. Looping improves pressure, reduces stagnation, and maintains service during repairs.

A pump installed within the distribution system to raise pressure or move water into a higher-pressure zone or elevated area. It is typically controlled by downstream pressure or flow.

A graph showing the relationship between a pump's flow rate and the head it produces, along with efficiency and power requirements. The point where it crosses the system curve is the operating point.

A plot of the head required to move various flow rates through a given piping system, including static lift and friction losses. The pump operates where the system curve intersects the pump curve.

The flow and head at which a specific pump actually runs in a specific system, found where the pump curve meets the system curve. Changing valves, speed, or demand shifts this point.

The absolute pressure margin at a pump suction that keeps water from vaporizing as it enters the impeller. Insufficient NPSH available compared with NPSH required causes cavitation.

Formation and collapse of vapor bubbles in water at low-pressure points inside a pump or pipe. It causes noise, vibration, pitting damage to the impeller, and reduced capacity.

An electronic controller that varies the speed of an electric motor by changing the frequency of power supplied to it. On pumps it allows smooth flow and pressure control and saves energy at partial demand.

A pressure wave caused by a sudden change in flow velocity, such as rapid valve closure or pump trip. It can produce damaging high and low pressures and requires surge protection.

A tank raised on a tower or standpipe so that its water surface sets the pressure in the zone it serves. It supplies fire flow, absorbs demand swings, and keeps pumps from cycling.

A valve on a tank inlet that closes when the tank reaches a set high level and reopens as the level drops. It prevents overflow and controls tank filling.

A valve that automatically lowers higher upstream pressure to a steady, lower downstream pressure. It is commonly used at zone boundaries and at customer services to protect plumbing and fixtures.

The time needed to replace the full volume of water in a storage tank through normal demand. Long turnover times lead to stagnant water, low disinfectant residual, and water quality complaints.

The concentration of disinfectant, usually free chlorine or chloramine, remaining in water as it travels through the distribution system. It must be maintained to prevent regrowth of microorganisms.

A measure of disinfection strength calculated by multiplying disinfectant concentration (C) by contact time (T). Required CT values depend on disinfectant type, water temperature, pH, and target pathogen.

Any actual or potential link between the potable water system and a source of nonpotable water or contamination. Uncontrolled cross-connections can allow backflow and cause illness.

Reverse flow of water or other substances into the potable system. Backsiphonage is driven by negative pressure, while backpressure is driven by a downstream pressure higher than supply pressure.

A physical separation between a potable water outlet and the flood level of a receiving vessel. It is the most reliable form of backflow protection because no mechanical parts can fail.

A testable backflow preventer with two check valves and a relief valve between them that discharges if a check fails. It protects against both backsiphonage and backpressure hazards.

A planned procedure in which valves are closed to force water to travel one direction at high velocity through a main, scouring sediment and biofilm. It is more effective than conventional flushing.

Making a new service connection to a main that is still under pressure, using a tapping machine and valve. It avoids shutting down the main and interrupting service to customers.

The pipe that carries water from the distribution main to a customer's property or meter. It includes the corporation stop, curb stop, meter, and associated fittings.

A valve on the customer service line, usually near the property line, used to shut off water for repairs or nonpayment. It is normally operated by the utility with a special key.

The scheduled opening and closing of distribution valves to confirm they work and to free them from corrosion and sediment. Regular exercising helps ensure valves close fully during emergencies.

A water sample collected in a sterile container and analyzed for total coliform bacteria and E. coli to verify treatment and distribution integrity. Sampling sites and frequency are set by regulation.

A federal rule setting monitoring and public notice requirements for coliform bacteria in drinking water. Routine positives trigger repeat sampling, and certain results require correction and notification.

The required process of informing customers when a drinking water violation or health risk occurs. It specifies timing, delivery method, and content based on the severity of the situation.

An annual report that utilities must deliver to customers summarizing water quality, contaminant results, sources, and compliance status. It must be distributed by a set deadline each year.

A documented record tracking a sample from collection through transport and laboratory analysis. It shows who handled the sample and when, proving the results are legally defensible.

A space large enough to enter, with limited entry or exit, not designed for continuous occupancy, such as a vault or wet well. Entry requires permits, atmospheric testing, and a standby attendant.

A safety procedure that isolates energy sources and applies locks and tags before maintenance, preventing accidental startup or release of stored energy. Only the person who applied a lock removes it.