Water Treatment

Action Level (AL)

The concentration of a contaminant which, if exceeded, triggers treatment or other requirements which a water system must follow.

Maximum Contaminant Level (MCL)

The highest level of a contaminant allowed in drinking water. Set as close to the MCLGs as feasible using the best available treatment technology.

Maximum Contaminant Level Goal (MCLG)

The level of a contaminant in drinking water below which there is no known or expected risk to health. Allow for a margin of safety.

Maximum Residual Disinfectant Level (MRDL)

The highest level of a disinfectant allowed in drinking water. There is convincing evidence that addition of a disinfectant is necessary for control of microbial contaminants.

Maximum Residual Disinfectant Level Goal (MRDLG)

The level of a drinking water disinfectant below which there is no known or expected risk to health. They do not reflect the benefits of the use of disinfectants to control microbial contaminants.

Nephelometric Turbidity Units (NTU)

A measure of the cloudiness (turbidity) of the water.

Parts Per Trillion (PPT)

One part per trillion is like one drop in one trillion drops of water, or about 1 inch in 16 million miles (about 67 trips around Earth).

Parts Per Billion (ppb)

One part per billion in water is like one drop in one billion drops of water, or about one inch in about 16,000 miles.

Parts Per Million (ppm)

One part per million is like one drop in one million drops of water, or about one inch in 16 miles.

Public Water System Identification (PWSID)

A unique identifier for each public water system.

Treatment Technique (TT)

A required process intended to reduce the level of a contaminant in drinking water.

Nitrate

NO3-

Total Trihalomethanes

TTHMs

Total Haloacetic Acids

HAA

Chloramine

NH2Cl

Coagulation

Adding positive-charge chemicals (such as aluminum sulfate or iron salts) to raw water to neutralize the negative charge of dirt and suspended particles. Results in destabilization and clumping of fine, negatively charged suspended particles into visible microflocs or "pin flocs" (typically around 50 µm in size) so they can be easily separated from the water.

Floculation

Gentle mixing of the water so neutralized particles bind together into larger, heavier clumps called floc.

Sedimentation

Allows gravity to pull the heavy floc particles down to the bottom of the treatment tank, separating them from the clearer water above.

Filtration

Passing the clear upper water through layers of sand, gravel, charcoal, or specialized membranes to remove remaining microscopic impurities and dissolved particles.

Disinfection

Adding chemical agents (like chlorine or chloramine) or physical treatments (like ultraviolet light or ozone) to kill any remaining bacteria, viruses, and parasites

Geometric mean

a type of average used in bacteria and water quality testing to smooth out extreme highs and lows in data.

Most probable number

a statistical method used to estimate the concentration of viable bacteria or microorganisms in water, food, or liquid samples

What is turbidity?

A measure of how cloudy water is due to suspended particles. It is important for evaluating treatment performance and filtration.

What is pH?

A measure of how acidic or basic water is.

What is water hardness?

Primarily the concentration of dissolved calcium and magnesium ions.

What is alkalinity?

Water's capacity to neutralize acids, primarily through bicarbonate and carbonate in typical drinking water.

What does conductivity measure?

How readily water conducts electricity, which is related to dissolved ions.

Why is chlorine residual monitored?

To verify that a disinfectant residual is maintained in the distribution system to help protect against microbial contamination.

What is the difference between free and total chlorine?

Free chlorine is available for disinfection; total chlorine includes free chlorine plus combined chlorine, such as chloramines.

Why is instrument calibration important?

It helps ensure measurements are accurate and traceable to appropriate standards.

What is a spectrophotometer used for?

Measuring light absorbance to determine the concentration of substances using an appropriate analytical method.

Why are SOPs important?

They promote consistent, repeatable testing and help ensure quality and regulatory compliance.

Purpose of adding lime

Removes calcium and magnesium from water to soften it and reduce hardness.

Purpose of adding aluminum sulfate

Removes dissolved organic material and assists in coagulation during the water treatment process.

Purpose of adding powder activated carbon

Improves water taste and odor by adsorbing impurities and contaminants during treatment.

Purpose of adding chloroamine

Disinfects the water, but must be kept within a safe level because it is toxic to humans.