Water Treatment Operator Class I key terms

The cloudiness of water caused by suspended particles such as clay, silt, organic matter, and microorganisms. It scatters light and is measured in nephelometric turbidity units. High turbidity shields pathogens from disinfection and must be removed.

The water's capacity to neutralize acid, coming mainly from bicarbonate, carbonate, and hydroxide ions. It buffers pH and gives coagulants such as alum something to react with, so low alkalinity can make coagulation difficult and depress pH.

A scale from 0 to 14 expressing how acidic or basic water is, based on hydrogen ion concentration. It affects coagulation, disinfection efficiency, corrosion of pipes, and whether treatment chemicals work as intended.

Water held in the pores and cracks of soil, sand, and rock beneath the surface. It is usually clearer and more consistent in quality than surface water but can carry dissolved minerals, iron, manganese, and contamination from land use.

Water in rivers, lakes, reservoirs, and streams that is open to the atmosphere and to runoff. It varies widely in turbidity, temperature, and microbial load with weather and seasons, so it almost always needs full treatment.

The land area that drains runoff into a particular river, lake, or reservoir. Protecting the watershed from sewage, farm runoff, and erosion reduces the cost and difficulty of treating the water it supplies.

An underground layer of rock or sediment that holds and transmits enough water to supply wells or springs. Its yield and water quality depend on the material and on how quickly recharge reaches it.

The concentration of dissolved calcium and magnesium, usually reported as milligrams per liter of calcium carbonate. Hard water leaves scale in pipes and heaters and reacts with soap, but it also buffers the water and reduces corrosion.

The process of adding a chemical such as alum or ferric chloride and mixing it rapidly so tiny particles lose their repelling charges and begin to clump. It is the first step in removing turbidity and color.

Brief, violent mixing right after coagulant is added, usually lasting 30 to 60 seconds. Its purpose is to spread the chemical through the water at once so particles are destabilized evenly before gentle flocculation begins.

Slow, gentle stirring that lets destabilized particles collide and stick together into larger, heavier clumps called floc. Time and mixing energy must be right: too little and floc stays small, too much and it shears apart.

A tank or clarifier where water moves slowly enough for floc and other solids to settle to the bottom. Sludge is collected and removed, and clearer water flows over the weirs toward filtration.

The layer of accumulated floc that forms in a clarifier, especially in upflow solids-contact units. Water rises through it and particles are trapped and swept out, making the blanket itself part of the treatment process.

The granular material, usually sand, anthracite, or both in layers, through which water passes to remove remaining particles. Media grain size, depth, and uniformity control how well the filter performs and how often it must be backwashed.

Reversing the flow of water upward through a filter, often with air scour, to break up the media and flush trapped solids to waste. It is started when headloss or effluent turbidity reaches a set limit.

The loss of pressure or water level as water is forced through a filter or pipe by friction and by the solids caught in the media. Rising headloss signals that the filter is loading up and needs backwashing.

The point in a filter run when particles pass through the media and appear in the finished water, shown by rising effluent turbidity. It usually means the filter needs backwashing or that the media has a problem.

A chlorine-resistant protozoan parasite that causes gastrointestinal illness and spreads through feces-contaminated water. Because chlorination alone does not control it, filtration plus other barriers such as UV or ozone are needed.

A measure of disinfection strength equal to the disinfectant residual concentration in mg/L multiplied by the contact time in minutes. Required CT varies with disinfectant, temperature, pH, and the organism being targeted.

The amount of chlorine still active in the water after the demand has been satisfied. It is the form that actually kills microorganisms and must be maintained throughout the distribution system to prevent regrowth.

The amount of chlorine consumed by microorganisms, organics, iron, manganese, and other substances in the water before a measurable residual can remain. It must be satisfied first before any protective residual is left.

A group of disinfection byproducts, including chloroform, formed when chlorine reacts with natural organic matter. Total THM concentrations are limited by regulation and rise with higher organic levels, temperature, pH, and contact time.

Another group of regulated disinfection byproducts formed when chlorine reacts with organic material in the water. HAA5 refers to five specific acids whose combined concentration has a maximum contaminant level.

Adding chlorine at points within the distribution system, such as pump stations or storage tanks, to restore residual that has decayed. It helps keep disinfection throughout long lines while limiting byproduct formation at the plant.

Any temporary or permanent link between the drinking water system and a source of nonpotable water or contamination. If backflow occurs, the contaminant can enter the pipes, so each connection needs an appropriate control device.

A pressure surge caused by a sudden change in flow, such as a valve closing quickly or a pump stopping without a controlled shutdown. It can burst pipes and damage fittings and must be controlled by design and operating practice.

The rate at which the volume of water in a tank is replaced by flow through it. Poor turnover, low residual, and warm water can let disinfection decay and allow bacterial or nitrification problems to develop.

The unit used to report turbidity measured with a nephelometer, which detects light scattered by particles at a set angle. It is the standard unit for treatment goals and regulatory limits on filter effluent.

A standard bench test in which several beakers of raw water receive different coagulant doses and are mixed through rapid mix, flocculation, and settling. Comparing the results shows which dose and pH give the best settled clarity.

The documented record of who collected a sample, when, where, and every hand that has held it since. Gaps or missing signatures can make the laboratory result useless in enforcement or legal action.

The theoretical time water stays in a basin or pipe, found by dividing the volume by the flow rate. It matters for settling, disinfection contact, and chemical reactions, and must be calculated in consistent units.

The calculation pounds per day equals concentration in mg/L times flow in million gallons per day times 8.34. Operators use it to convert a desired dose into the actual weight of chemical to feed.

A flow rate unit equal to one million gallons of water passing a point in 24 hours. Plant and system capacities and the pounds formula are commonly stated in this unit.

The highest concentration of a regulated contaminant allowed in drinking water delivered to consumers, set by EPA under the Safe Drinking Water Act. Some contaminants instead have a required treatment technique.

An annual report that every community water system must give its customers, listing the source of the water, detected contaminants and their levels, compliance status, and health information. Also called the annual drinking water quality report.

An enclosed space with limited entry and exit that is not designed for continuous occupancy, such as a storage tank, vault, or wet well. Entry requires atmosphere testing, ventilation, a permit, and a standby attendant.

A federal rule requiring systems using surface water, or groundwater under direct influence of surface water, to filter and disinfect so pathogens are removed or inactivated. It sets turbidity and CT requirements and requires qualified operators.