Glossary of Water-Testing Terms

E. coli (Escherichia coli)

E. coli is a Gram-negative bacterium found naturally in the intestines of warm-blooded animals. Most strains are harmless, but pathogenic strains can cause severe foodborne illness. Its presence in drinking water is a regulatory indicator of fecal contamination and elevated public-health risk.

The cell is rod-shaped, roughly 1–3 μm long and 0.5 μm in diameter. Detection in water is required under the U.S. EPA Safe Drinking Water Act and WHO Guidelines. The AquaVial EX E. coli Test Kit detects E. coli at 1 CFU/ml in 9 hours.

Total Coliform

Total coliform is a broad group of Gram-negative, rod-shaped bacteria — including E. coli, Klebsiella, Enterobacter, and Citrobacter — used as a general indicator of water hygiene. Coliforms are easier to detect than specific pathogens, so they serve as a screening signal: if coliforms are present, more dangerous bacteria may be too.

The EPA Total Coliform Rule requires that no coliforms be detected in any 100-mL sample of public drinking water. Private wells are unregulated federally but follow the same recommended standard. AquaVial's Total Coliform 8-Pack detects coliforms at 1 CFU/ml.

Fecal Coliform

Fecal coliform is the subset of total coliform bacteria that originates specifically in the intestines of warm-blooded animals. E. coli is the dominant species in this group. Fecal coliform contamination in water indicates direct fecal pollution and a higher risk of pathogenic illness than general total coliform.

Pseudomonas aeruginosa

Pseudomonas aeruginosa is an opportunistically pathogenic Gram-negative bacterium that thrives in moist environments — hot tubs, showers, sinks, swimming pools, and dental waterlines. Exposure can cause hot-tub folliculitis, swimmer's ear, and respiratory infections in immunocompromised individuals.

Pseudomonas is highly resistant to chlorine and survives in biofilm even after disinfection. AquaVial's Hot Tub, Shower & Pool Test Kit detects Pseudomonas at 1 CFU/ml.

Legionella pneumophila

Legionella pneumophila is a Gram-negative bacterium responsible for Legionnaires' disease — a severe form of pneumonia — and Pontiac fever. It grows in warm-water systems including cooling towers, hot tubs, hot-water tanks, and decorative fountains. The primary exposure route is inhalation of contaminated aerosols.

CDC guidelines recommend periodic Legionella monitoring in healthcare facilities, hotels, and high-risk water systems. Legionella is notoriously difficult to detect via standard plate methods, which is why rapid nanoparticle-based screening is valuable.

Biofilm

A biofilm is a structured community of microorganisms embedded in a self-produced matrix of extracellular polymeric substances, attached to a surface. Biofilms form on the inside of pipes, dental waterlines, shower heads, and hot tub plumbing.

Biofilms protect microorganisms from disinfectants, making them roughly 100× more resistant to chlorine than free-floating cells. Disrupting biofilm typically requires mechanical cleaning combined with shock chlorination.

Salmonella enterica

Salmonella enterica is a Gram-negative, rod-shaped bacterium that causes salmonellosis — a foodborne illness with symptoms including diarrhea, fever, and abdominal cramps. Contaminated water is a less common but documented transmission route. Cell size: 2–3 μm long, 0.6–0.7 μm in diameter.

Staphylococcus aureus

Staphylococcus aureus is a Gram-positive, spherical (coccus) bacterium known to cause skin and soft-tissue infections. Most commonly transmitted via direct contact, but contaminated recreational water and biofilm in showers or sinks can serve as exposure sources.

CFU (Colony Forming Unit)

A colony forming unit is the basic unit of measurement for viable microorganisms in microbiology. One CFU represents a single bacterial cell — or a cluster of cells — that grows into one visible colony when cultured on agar. Expressed per volume (CFU/mL) or per area.

The lower the CFU/mL detection limit of a test kit, the more sensitive it is. AquaVial detection limits range from 1 CFU/ml (Coliform, E. coli, Pseudomonas) to 500 CFU/ml (general bacteria screening) depending on the assay, sample volume, and incubation time.

MPN (Most Probable Number)

Most Probable Number is a statistical method for estimating bacterial concentration based on multiple-tube dilution assays. Reported as MPN/100mL for water samples. MPN and CFU are roughly equivalent but derived from different methodologies (statistical vs. colony-counting).

The IDEXX Quanti-Tray method, an EPA-approved reference method for E. coli enumeration, reports results as MPN.

CFU/mL vs. CFU/100mL

CFU/mL measures bacteria per milliliter; CFU/100mL measures per 100 milliliters. The conversion is straightforward: 10 CFU/mL = 1,000 CFU/100mL. EPA drinking-water standards typically use CFU/100mL for low-concentration testing; pool and hot-tub standards use CFU/mL or CFU/100mL depending on jurisdiction.

HPC (Heterotrophic Plate Count)

Heterotrophic Plate Count is the standard laboratory method for measuring total bacterial concentration in water. A water sample is plated on nutrient agar, incubated at 35°C for 48 hours, and visible colonies are counted. Results are reported in CFU/mL.

HPC is the regulatory reference method for general bacterial monitoring but cannot distinguish pathogenic from harmless bacteria. AquaVial's color-change assays correlate strongly with HPC results, with the advantage of 30-minute to 24-hour result times instead of 48 hours.

Chromocult Coliform Agar

Chromocult is a selective and chromogenic culture medium used in laboratories to simultaneously detect and differentiate E. coli and other coliforms in water. Coliform colonies appear pink/red; E. coli colonies appear dark blue/purple. It is one of the regulatory gold-standard methods for water-quality plate counts.

AquaVial's EX 24-hour coliform vial was field-validated against Chromocult at Valens Lake Conservation Area, achieving 100% concordance across 36 sample events.

IDEXX Quanti-Tray (Method M548)

The IDEXX Quanti-Tray Method is an EPA-approved laboratory method for enumerating E. coli and total coliforms in water. Uses a sealed tray with defined wells; results read after 24-hour incubation at 35°C. Reports as MPN/100mL.

CAWT at Fleming College used IDEXX Quanti-Tray as the reference method for the 2025 independent verification of AquaVial EZ, confirming detection at concentrations as low as 12 CFU/100mL. See our Research & Data page for the full study.

ATCC (American Type Culture Collection)

ATCC is a non-profit organization that maintains and distributes standardized biological reference materials including bacterial, fungal, and viral cultures. ATCC reference strains are used to validate water-testing methods because they provide reproducible, well-characterized organisms.

Examples used in AquaVial validation work: E. coli ATCC 11229, Pseudomonas aeruginosa ATCC 15442, Bacillus megaterium ATCC 21209, Salmonella enterica ATCC 10708.

Reference Method / Gold Standard

A reference method is a regulatory-approved laboratory procedure used as the comparison baseline for evaluating new test methods. Common reference methods for water testing include HPC, Chromocult, IDEXX Quanti-Tray, and membrane filtration with selective media.

New test kits must demonstrate concordance with a reference method to gain regulatory and customer trust.

Detection Limit (Limit of Detection, LoD)

Detection limit is the lowest concentration of an analyte (e.g., bacteria) that a test method can reliably distinguish from zero. Expressed as CFU/mL or CFU/100mL. A lower detection limit means a more sensitive test.

AquaVial detection limits range from 1 CFU/ml (Coliform, E. coli, Pseudomonas) to 500 CFU/ml (general total-bacteria screening) depending on the kit, sample volume, and incubation time. See Technical Data Sheets for per-product detection limits.

Sample Volume

Sample volume is the amount of water tested. Larger sample volumes generally improve sensitivity — a kit can detect lower concentrations in a 100mL sample than in a 5mL sample, because there are more cells available to detect.

Many AquaVial kits include a filter-concentrate step that effectively increases sample volume by 20× or more.

Incubation Period

The incubation period is the time a water sample must be held at a specific temperature for the test reaction to develop. AquaVial incubation periods range from 30 minutes to 48 hours depending on the assay.

Standard HPC plate counts require 48 hours; AquaVial's nanoparticle-based color-change assays typically resolve in 30 minutes to 24 hours, allowing same-day action on contamination findings.

False Positive

A false positive is a test result that indicates contamination when none is present. False positives lead to unnecessary actions like water-system shutdown or remediation.

AquaVial's April 2026 stability study recorded zero false positives across 30 individual tests on 13 production lots.

False Negative

A false negative is a test result that indicates no contamination when contamination is in fact present. False negatives are dangerous because they leave hazards undetected.

AquaVial's 2025 CAWT verification study recorded zero false negatives in triplicate testing at concentrations from 12 to 101 CFU/100mL.

Sensitivity vs. Specificity

Sensitivity is the probability that a test correctly identifies a positive sample (true positive rate); specificity is the probability that it correctly identifies a negative sample (true negative rate). High sensitivity reduces false negatives; high specificity reduces false positives.

Filter-Concentrate Workflow

A filter-concentrate workflow is a sample-preparation step in which a relatively large water sample (e.g., 100mL) is passed through a filter that captures bacteria, then the captured cells are eluted into a much smaller volume. This concentrates the bacteria, lowering the effective detection limit.

The AquaVial EX kit uses a filter-concentrate workflow to detect as low as 1 CFU per 10mL of source water.

Free Chlorine

Free chlorine is the concentration of unreacted chlorine available to disinfect water. Measured in mg/L (or ppm). Public drinking water typically maintains 0.2–4.0 mg/L free chlorine; pool water guidelines suggest 1–3 mg/L.

Free chlorine kills most bacteria within minutes. Biofilm-protected microorganisms (like Pseudomonas and Legionella) are far more resistant, which is why periodic bacterial testing is essential even in chlorinated systems.

Total Chlorine

Total chlorine is the sum of free chlorine plus combined chlorine — chlorine that has reacted with ammonia or organic matter to form chloramines. The difference between total chlorine and free chlorine indicates chloramine load, which can cause eye irritation in pools and a chlorinous odor.

UV Disinfection

UV (ultraviolet) disinfection uses UV-C light to damage microbial DNA, rendering bacteria, viruses, and protozoa unable to reproduce. UV is widely used for well-water treatment and point-of-use disinfection.

UV efficacy depends on water clarity, flow rate, lamp intensity, and contact time. AquaVial's 2021 UV study showed disinfection efficacy varies sharply with flow rate, often failing to meet the advertised 99.9% kill claim in real-world conditions. Periodic post-UV verification testing is recommended.

EPA Standard (Drinking Water)

The EPA Total Coliform Rule establishes the U.S. federal standard that no coliform bacteria be detected in any 100-mL sample of public drinking water. The Maximum Contaminant Level (MCL) for E. coli in drinking water is zero.

Private wells are not federally regulated but are recommended to meet the same standards. Some states require periodic well-water testing under state law.

WHO Guidelines for Drinking-Water Quality

The WHO Guidelines establish international recommendations for safe drinking water. The microbial guideline recommends that E. coli not be detectable in any 100-mL sample of treated water entering or within the distribution system.

WHO is the standard reference internationally and informs national drinking-water regulations in most countries.

ISO 9001:2015

ISO 9001:2015 is the international standard for quality management systems. It establishes requirements for documenting, implementing, and continuously improving quality processes across an organization. ISO 9001 certification is independently audited and renewed every three years.

ExactBlue Technologies Inc. (manufacturer of AquaVial) is ISO 9001:2015 certified by BSCIC Certifications Pvt. Ltd. — Certificate No. BN22048/20927, valid through March 29, 2029.

ISO 17025:2017

ISO 17025:2017 is the international standard for the competence of testing and calibration laboratories. It is more stringent than ISO 9001 because it specifically addresses laboratory technical competence — equipment calibration, method validation, measurement uncertainty, and result reliability.

CAWT at Fleming College holds ISO 17025:2017 accreditation and provided independent verification of AquaVial EZ in September 2025.

WHMIS

WHMIS (Workplace Hazardous Materials Information System) is Canada's federal hazard-communication standard for workplace chemicals. WHMIS 2015 aligned Canadian standards with the global GHS framework.

WHMIS-compliant Safety Data Sheets are required for all hazardous workplace chemicals. AquaVial publishes WHMIS-compliant SDS for every active product.

GHS & OSHA

GHS (Globally Harmonized System of Classification and Labelling of Chemicals) is the international standard for hazard communication. In the United States, GHS is incorporated into OSHA's Hazard Communication Standard. GHS specifies the format of Safety Data Sheets and pictogram-based labels.

ADA & CDC Dental Waterline Guidelines

The American Dental Association (ADA) and U.S. Centers for Disease Control and Prevention (CDC) recommend that dental unit waterlines maintain a heterotrophic plate count of ≤500 CFU/mL during patient treatment.

This threshold matches the EPA standard for safe drinking water and protects both patients and dental professionals from exposure to opportunistic pathogens in dental-unit biofilm.

β-galactosidase (Beta-galactosidase)

β-galactosidase is an enzyme produced by coliform bacteria (and certain other bacteria) that hydrolyzes β-galactosides. It serves as a diagnostic marker for coliform presence in water.

AquaVial's coliform test kits exploit β-galactosidase activity by combining it with a chromogenic substrate (CPRG) to produce a visible color change when bacteria are present.

CPRG (chlorophenol red-β-D-galactopyranoside)

CPRG is a chromogenic substrate for β-galactosidase. When unreacted, CPRG appears yellow-orange. When β-galactosidase (from bacterial cells) hydrolyzes CPRG, it releases chlorophenol red, producing a visible color shift from yellow to red/purple.

This is the core chemistry behind AquaVial's coliform and E. coli detection kits.

Gold Nanoparticle / Gold Nanoshell

Gold nanoparticles are colloidal particles of metallic gold suspended in solution, typically 10–100 nm in diameter. Their surface chemistry can be modified ("functionalized") to bind specific molecules or microbial cell surfaces. The optical properties of gold nanoparticles shift dramatically with aggregation state, producing measurable color changes.

AquaVial's AquAssay reagent uses functionalized gold nanoparticles to bind bacterial cell walls. The chemistry was developed at the University of Waterloo by Dr. Shazia Tanvir and Dr. William A. Anderson and published in 2017 (Enzyme and Microbial Technology). International patent application: PCT/CA2021/050834.

Functionalized Nanoparticles

Functionalized nanoparticles are nanoparticles whose surfaces have been chemically modified to attach to specific target molecules. Surface chemistry — charge, hydrophobicity, conjugated ligands — controls what the nanoparticle binds.

AquaVial uses CTAB-functionalized gold nanoshells engineered to preferentially bind bacterial cell surfaces.

Aptamer

An aptamer is a short DNA or RNA molecule selected to bind a specific target with high affinity and specificity — sometimes called "synthetic antibodies." In water testing, aptamers can detect specific pathogens by binding their surface proteins.

AquaVial's SARS-CoV-2 detection research (2022, Talanta, with McMaster University) used aptamer-functionalized gold nanoparticles — evidence that the AquAssay platform extends beyond bacterial detection.

Colorimetric Assay

A colorimetric assay is a test method that produces a visible color change in proportion to the concentration of an analyte. Colorimetric assays can be read visually (with reference to a color chart) or quantitatively (with a spectrophotometer).

They are well-suited to point-of-use testing because they require no specialized equipment. All AquaVial test kits are colorimetric assays.