Glossary

Water and wastewater operator glossary

Clear definitions of the terms that show up most on the water and wastewater operator exams. Each one is written plainly, so you can find exactly what a word means and why it matters at the plant.

Water quality

Turbidity: How cloudy water is, from tiny suspended particles. High turbidity can hide germs from disinfection, so it is watched closely and held under a strict limit.
pH: A scale from 0 to 14 for how acidic or basic water is, where 7 is neutral. pH changes how well chlorine works and whether water eats at pipes.
Alkalinity: Water's ability to resist a change in pH, mostly from carbonates. It acts as a buffer and matters for coagulation and corrosion control.
Total dissolved solids (TDS): The total dissolved minerals and salts in water, measured in mg/L. High TDS can affect the taste and the treatment.
Dissolved oxygen (DO): The amount of oxygen dissolved in water, in mg/L. In wastewater, the microorganisms in activated sludge need enough of it to break down waste.
Parts per million (ppm): A way to state a very small amount, one part in a million. In water, 1 ppm is about the same as 1 mg/L.
Hardness: The amount of calcium and magnesium dissolved in water. Hard water leaves scale, which is a nuisance more than a health risk.
Coliform bacteria: Indicator organisms tested for in drinking water. Finding them is a warning that contamination may have reached the system.

Treatment steps

Coagulation: Adding a chemical that makes tiny suspended particles clump together so they can be removed. The first step in treating cloudy surface water.
Flocculation: Gentle mixing after coagulation that lets the small clumps grow into larger, heavier floc that settles faster.
Sedimentation: Letting the heavy floc and solids settle to the bottom of a basin by gravity, so the clearer water above can move on.
Filtration: Passing water through sand or other media to strain out the fine particles that settling did not catch.
Aeration: Adding air to water. In wastewater it feeds the microorganisms; in drinking water it can drive off gases and odors.
Disinfection: Killing or inactivating disease-causing organisms, most often with chlorine, before water is delivered or effluent is released.

Disinfection and chlorine

Chlorine dose: The total amount of chlorine added to the water, measured in mg/L.
Chlorine demand: The chlorine used up by reactions in the water before any is left over.
Chlorine residual: The chlorine left after demand is met, which keeps protecting the water downstream. Dose equals demand plus residual.
Chloramine: A longer-lasting disinfectant made by combining chlorine with ammonia. Some systems use it to hold a residual farther out in the pipes.

Wastewater

Influent: The wastewater flowing into a treatment plant.
Effluent: The treated water flowing out of a plant.
Activated sludge: A treatment process that uses microorganisms and added air to break down waste dissolved in the water.
Clarifier: A tank where solids settle out of the water so the cleaner water above can move on.
Sludge: The settled solids collected during treatment, before they are processed further.
Biosolids: The treated solids from wastewater, sometimes reused on land under strict rules.
Collection system: The sewers and lift stations that carry wastewater from homes and businesses to the plant.
Lift station: A pump station that raises wastewater to a higher point so it can keep flowing to the plant by gravity.

Water sources and delivery

Potable water: Water that is safe to drink.
Groundwater: Water pumped from underground through wells.
Surface water: Water drawn from lakes, rivers, or reservoirs.
Distribution system: The pipes, pumps, and storage tanks that carry treated water to customers.
Storage: Tanks that hold treated water to cover busy hours, steady the pressure, and keep a reserve for firefighting.

Units and measures

MGD: Million gallons per day, a common way to report the flow through a plant.
GPM: Gallons per minute.
GPD: Gallons per day.
mg/L: Milligrams per liter, the standard unit for a concentration in water. About equal to ppm.
Cubic foot: A volume one foot on each side. One cubic foot of water holds 7.48 gallons and weighs about 62.4 pounds.
Detention time: How long, on average, water stays in a tank or basin. It is the tank volume divided by the flow, and it sets how long treatment has to work.