Water test results are a laboratory report showing the measured concentrations of specific contaminants and quality parameters in your water supply, compared against EPA Maximum Contaminant Levels and other health-based standards. Understanding these results allows homeowners to determine whether their water is safe to drink, identify parameters that need attention, and make informed decisions about water treatment systems.

How to Read a Laboratory Water Test Report

A water test report from an accredited laboratory contains more information than most homeowners expect. Understanding the layout and terminology is the first step to interpreting your results.

Key Sections of a Lab Report

A typical water test report from AATLS includes the following sections:

• Laboratory information: The lab name, address, accreditation numbers, and contact information. This identifies who performed the testing and confirms the laboratory’s qualifications.
• Client and sample information: Your name, the sample identification, collection date and time, date received by the laboratory, and the sample location or description.
• Analytical results table: The core of the report. Each row lists a parameter (what was tested), the result (the measured concentration), the units of measurement, the method detection limit (MDL) or reporting limit (RL), and the applicable regulatory standard.
• Quality control summary: Information about the QC samples analyzed with your sample, including method blanks, laboratory control samples, and duplicates.
• Chain of custody: Documentation of who handled the sample from collection through analysis.
• Notes and qualifiers: Data flags or narrative comments that provide additional context for specific results.

Understanding Units of Measurement

Water test results use several different units of measurement, and understanding them is essential for interpreting your results:

• mg/L (milligrams per liter): The most common unit for water chemistry results. One mg/L is equivalent to one part per million (ppm). Used for parameters like nitrate, fluoride, hardness, and TDS.
• ug/L (micrograms per liter): Equal to parts per billion (ppb). Used for trace contaminants like lead, arsenic, and mercury. There are 1,000 micrograms in one milligram, so 10 ug/L equals 0.01 mg/L.
• ng/L (nanograms per liter): Equal to parts per trillion (ppt). Used for ultra-trace contaminants like PFAS. There are 1,000 nanograms in one microgram. The new EPA standard for PFOA is 4 ng/L, which is 4 parts per trillion.
• CFU/100mL (colony forming units per 100 milliliters): Used for bacterial counts. Indicates the number of viable bacteria detected in a 100 mL sample volume.
• NTU (nephelometric turbidity units): Used for turbidity, which measures how cloudy or hazy the water is.
• SU (standard units): Used for pH, which is measured on a scale from 0 to 14.

Understanding Detection Limits and “Non-Detect” Results

One of the most common sources of confusion on lab reports is the concept of detection limits. Every analytical method has a minimum concentration it can reliably measure. Results below this threshold are reported as “non-detect” (ND), “less than” the detection limit (e.g., <0.001 mg/L), or “below reporting limit” (BRL).

A non-detect result does not necessarily mean the contaminant is completely absent. It means the concentration is below the level the laboratory method can reliably quantify. For most practical purposes, non-detect results for regulated contaminants mean the water meets the applicable standard for that parameter.

The method detection limit (MDL) is the lowest concentration that can be detected with 99 percent confidence that the result is greater than zero. The reporting limit (RL) or practical quantitation limit (PQL) is typically set at a higher concentration where the laboratory can measure results with a defined level of accuracy and precision. AATLS reports results against both the MDL and the applicable regulatory standard so you can see the full picture.

Common Water Quality Parameters Explained

Below is a detailed explanation of the parameters most commonly included in residential water tests, what the numbers mean, and what levels should concern you as an Arizona homeowner.

pH

What it is: A measure of how acidic or alkaline your water is, on a scale from 0 (most acidic) to 14 (most alkaline), with 7 being neutral.

EPA guideline: 6.5 to 8.5 (secondary standard, not enforceable).

What your results mean:

• Below 6.5: Acidic water. Can corrode pipes and leach metals (lead, copper) from plumbing. May cause a metallic taste. Relatively uncommon in Arizona, where water tends to be alkaline.
• 6.5 to 8.5: Normal range. No action needed.
• Above 8.5: Alkaline water. Common in Arizona due to dissolved minerals. Can cause scale buildup in pipes and water heaters, reduce the effectiveness of chlorine disinfection, and contribute to a bitter taste. Many Arizona water sources naturally measure 7.5 to 8.5 or slightly above.

Arizona context: Most Arizona groundwater is moderately alkaline, typically pH 7.2 to 8.2. This is a natural result of the carbonate and bicarbonate minerals in the region’s geology. Slightly alkaline water is generally not a health concern but can affect the performance of water treatment systems and the longevity of plumbing components.

Total Dissolved Solids (TDS)

What it is: The total concentration of dissolved minerals, salts, and organic matter in your water. TDS includes calcium, magnesium, sodium, potassium, bicarbonate, chloride, sulfate, and other dissolved substances.

EPA guideline: 500 mg/L (secondary standard).

What your results mean:

• Below 300 mg/L: Excellent. Water will taste clean and is unlikely to cause scaling or staining.
• 300-500 mg/L: Good. Acceptable for drinking water. Minor scaling may occur in hot water systems.
• 500-1,000 mg/L: Fair. You may notice a mineral taste. Scaling in pipes and water heaters becomes more significant. Consider a water softener or RO system.
• Above 1,000 mg/L: Poor. Water may have an objectionable taste. Significant scaling and potential staining. Treatment is recommended.

Arizona context: Arizona water typically has TDS levels ranging from 200 to over 1,500 mg/L depending on the source. Tucson Water reports TDS levels ranging from approximately 250 to 450 mg/L in its distribution system. Private wells in some areas of Pinal and Maricopa counties can exceed 2,000 mg/L. The Colorado River, which supplies much of central and western Arizona through the Central Arizona Project, has TDS levels of approximately 600 to 750 mg/L.

Hardness

What it is: The concentration of dissolved calcium and magnesium in your water, expressed as mg/L of calcium carbonate (CaCO3).

EPA guideline: No MCL. Water hardness is classified as:

• Soft: 0-60 mg/L
• Moderately hard: 61-120 mg/L
• Hard: 121-180 mg/L
• Very hard: Above 180 mg/L

What your results mean: Hardness is not a health risk at typical concentrations. However, hard water causes:

• White scale deposits on faucets, showerheads, and inside pipes.
• Reduced efficiency and shortened lifespan of water heaters (the Department of Energy estimates that scale buildup can reduce water heater efficiency by 25 to 30 percent).
• Difficulty lathering soap and shampoo.
• Spotting on dishes and glassware.
• Stiff, dull laundry.

Arizona context: Most Arizona water qualifies as “very hard” by USGS classification. Tucson groundwater typically measures 150 to 500 mg/L as CaCO3. Some wells in the Avra Valley and Santa Cruz Valley exceed 700 mg/L. If your results show hardness above 120 mg/L, a water softener can protect your plumbing and appliances. The average Arizona household spends approximately $300 to $500 more per year on plumbing maintenance, water heater replacement, and increased energy costs due to hard water compared to homes with treated water.

Total Coliform Bacteria

What it is: A group of bacteria that are widely found in the environment, including in soil, vegetation, and the intestines of warm-blooded animals. Total coliforms serve as indicator organisms: their presence in water suggests that a pathway exists for potentially harmful organisms to enter the water supply.

EPA standard: Total coliform positive is a violation under the Revised Total Coliform Rule. Any confirmed detection requires assessment and potentially corrective action.

What your results mean:

• Absent or negative: No coliform bacteria detected. This is the desired result.
• Present or positive: Coliform bacteria were detected. This does not necessarily mean the water will make you sick, but it indicates a potential contamination pathway. Follow-up testing and investigation are recommended. If you are on a private well, check the wellhead seal, the well cap, and the area around the well for potential contamination sources.

E. coli (Escherichia coli)

What it is: A specific type of coliform bacteria found in the intestines of humans and warm-blooded animals. E. coli in drinking water is a direct indicator of fecal contamination.

EPA standard: Zero tolerance. Any detection of E. coli in drinking water is a violation and indicates an immediate health risk.

What your results mean:

• Absent or negative: No E. coli detected. This is the desired result.
• Present or positive: This is a serious finding. Do not drink the water until the issue is resolved. Use bottled water for drinking and cooking. Contact your water system or well contractor immediately. Resample to confirm the result. If confirmed, the contamination source must be identified and eliminated, and the system must be disinfected (typically with shock chlorination for wells) before retesting.

Lead

What it is: A toxic heavy metal that enters drinking water primarily through corrosion of lead-containing plumbing materials, including lead service lines, lead solder used on copper pipes (common before 1986), and brass faucets and fittings.

EPA action level: 15 ug/L (ppb) at the tap. However, the EPA states that the maximum contaminant level goal (MCLG) for lead is zero, meaning there is no safe level of lead exposure.

What your results mean:

• Non-detect or below 1 ug/L: Excellent. Minimal lead exposure from your plumbing.
• 1-5 ug/L: Low but detectable. Consider flushing the tap for 30 seconds before using water for drinking or cooking, especially after extended periods of non-use.
• 5-15 ug/L: Moderate. Action is recommended, particularly if children under 6 or pregnant women are in the household. Consider a point-of-use filter certified for lead removal (NSF/ANSI Standard 53).
• Above 15 ug/L: Exceeds EPA action level. Install a lead-removal filter immediately. Investigate and address the source of lead in your plumbing. Consider replacing lead service lines or lead-soldered joints.

Arizona context: Lead in Arizona drinking water comes primarily from older plumbing rather than from the source water itself. Homes built before 1986 are most at risk due to the use of lead solder. Arizona’s alkaline water can actually provide some protection against lead leaching by forming a mineral scale inside pipes, but this protection is not guaranteed. The EPA’s Lead and Copper Rule Improvements (LCRI), finalized in 2024, require water systems to replace all lead service lines within 10 years. For private homes, however, responsibility falls on the homeowner.

Nitrate

What it is: A nitrogen compound that enters groundwater from agricultural fertilizers, animal waste, septic systems, and natural geological sources. Nitrate is one of the most common groundwater contaminants in the United States.

EPA MCL: 10 mg/L (as nitrogen).

What your results mean:

• Below 2 mg/L: Low. Typical background level for unimpacted groundwater.
• 2-5 mg/L: Slightly elevated. May indicate some influence from agricultural or septic sources. Not a health concern at this level but worth monitoring over time.
• 5-10 mg/L: Elevated. While below the MCL, this level suggests significant nitrate input from human activities. Monitor annually and investigate potential sources if levels are trending upward.
• Above 10 mg/L: Exceeds EPA MCL. Do not use this water for infant formula preparation. Nitrate at this level can cause methemoglobinemia (blue baby syndrome) in infants under 6 months. Adults are generally less susceptible but long-term exposure at elevated levels may have health effects. Treatment options include ion exchange, reverse osmosis, or blending with a low-nitrate source.

Arizona context: ADEQ has identified multiple areas in Arizona with elevated groundwater nitrate. Agricultural regions in Pinal County, the Safford Valley, the Buckeye-Arlington area, and parts of the Prescott Active Management Area have documented nitrate levels approaching or exceeding the MCL. Rural properties near farms, feedlots, or older septic systems are at higher risk. Nitrate does not decrease over time without treatment, as it is stable in groundwater, so an elevated result is not likely to improve without intervention.

Arsenic

What it is: A naturally occurring toxic element found in rocks, soil, and groundwater. Long-term exposure to arsenic in drinking water is associated with increased risk of cancer (skin, bladder, lung, kidney, liver), cardiovascular disease, diabetes, and developmental effects in children.

EPA MCL: 10 ug/L (ppb).

What your results mean:

• Below 3 ug/L: Low. Well below the MCL. Minimal health risk at this level.
• 3-10 ug/L: Detectable but below the MCL. The EPA’s MCLG for arsenic is zero, meaning any level carries some theoretical risk with long-term exposure. Some health experts recommend treatment at levels above 3-5 ug/L, particularly for households with children or pregnant women.
• 10-50 ug/L: Exceeds EPA MCL. Treatment is necessary. Point-of-entry arsenic adsorption systems or reverse osmosis systems are effective treatment options. Do not boil the water, as boiling concentrates arsenic rather than removing it.
• Above 50 ug/L: Significantly exceeds the MCL. Immediate treatment is essential. Consider using bottled water until a treatment system is installed and verified to be working. The old EPA MCL was 50 ug/L until it was lowered to 10 ug/L in 2006, and some Arizona water systems received compliance extensions during the transition.

Arizona context: Arizona is one of the states most affected by naturally occurring arsenic in groundwater. The USGS has documented that approximately 10 percent of Arizona wells sampled exceed the 10 ug/L MCL, with rates exceeding 30 percent in some areas including parts of the Tucson basin, the Verde Valley, and portions of Cochise and Pinal counties. Arsenic in Arizona groundwater is primarily inorganic arsenic (the more toxic form) released from volcanic and sedimentary rocks in the Basin and Range Province. Unlike contamination from human activities, naturally occurring arsenic cannot be eliminated at the source, so treatment is the only option for affected wells. Visit our water testing page to learn about arsenic testing options.

Fluoride

What it is: A naturally occurring mineral that strengthens tooth enamel at low concentrations but can cause health effects at elevated levels. Many municipal water systems add fluoride at approximately 0.7 mg/L for dental health.

EPA MCL: 4.0 mg/L. Secondary standard: 2.0 mg/L (for cosmetic effects).

What your results mean:

• Below 0.7 mg/L: Below the optimal level for dental health. Not a health concern.
• 0.7-2.0 mg/L: Normal range. Provides dental health benefits without cosmetic effects.
• 2.0-4.0 mg/L: Above the secondary standard. Long-term exposure may cause dental fluorosis (discoloration and pitting of tooth enamel) in children whose teeth are still developing. Consider treatment if young children are in the household.
• Above 4.0 mg/L: Exceeds the EPA MCL. Long-term exposure may cause skeletal fluorosis (bone pain and damage). Treatment (activated alumina, reverse osmosis, or bone char filtration) is recommended.

Arizona context: Natural fluoride levels in Arizona groundwater vary widely, from less than 0.5 mg/L to over 10 mg/L, depending on the local geology. Wells in the areas around Gila Bend, portions of the Tohono O’odham Nation, and parts of Cochise County have historically shown elevated natural fluoride. If your well water tests above 2.0 mg/L, the fluoride is almost certainly from natural geological sources rather than from any human activity.

Copper

What it is: A metal that enters drinking water primarily through corrosion of copper plumbing, which is the most common residential plumbing material in homes built after the 1960s.

EPA action level: 1.3 mg/L (1,300 ug/L).

What your results mean:

• Below 0.3 mg/L: Low. No action needed.
• 0.3-1.3 mg/L: Detectable copper leaching from plumbing. Flush the tap for 30 seconds before using water for drinking or cooking after extended periods of non-use. If the water has a blue-green tint or metallic taste, investigate the cause.
• Above 1.3 mg/L: Exceeds EPA action level. Short-term exposure above this level can cause gastrointestinal symptoms (nausea, vomiting, diarrhea). Investigate the source of copper (likely corroding plumbing) and consider pH adjustment or a corrosion control system.

Arizona context: Copper plumbing is nearly universal in Arizona homes. The slightly alkaline pH of most Arizona water provides some protection against copper corrosion, but aggressive water chemistry (low pH, high dissolved oxygen, high TDS) can accelerate corrosion. New copper plumbing tends to leach more copper during the first 1-2 years as a protective patina develops on the inside of the pipes. First-draw samples (collected after 6 hours of stagnation) provide the most accurate assessment of copper exposure.

PFAS (Per- and Polyfluoroalkyl Substances)

What they are: A group of thousands of synthetic chemicals used since the 1940s in industrial and consumer products including non-stick cookware, water-resistant fabrics, food packaging, and firefighting foam (AFFF). PFAS are called “forever chemicals” because they do not break down in the environment.

EPA MCLs (finalized April 2024):

• PFOA: 4.0 ng/L (ppt)
• PFOS: 4.0 ng/L (ppt)
• PFHxS: 10 ng/L (ppt)
• PFNA: 10 ng/L (ppt)
• GenX (HFPO-DA): 10 ng/L (ppt)
• Mixtures of PFHxS, PFNA, HFPO-DA, and PFBS: Hazard Index of 1

What your results mean:

• All PFAS non-detect: No PFAS detected above the method detection limit. This is the best possible result.
• PFAS detected but below MCLs: PFAS are present but below the federally enforceable limits. Given the very low MCLs, any detection warrants attention. Consider a point-of-use treatment system (granular activated carbon or reverse osmosis) as a precautionary measure.
• Any PFAS above its MCL: Exceeds the federal standard. Treatment is recommended. Granular activated carbon (GAC) and reverse osmosis (RO) are both effective at removing PFAS. Whole-house GAC systems cost $1,500 to $5,000 installed, and under-sink RO systems cost $200 to $500.

Arizona context: PFAS contamination in Arizona is concentrated around military installations and airports where AFFF was used. The most significant sites include areas near Davis-Monthan Air Force Base and Tucson International Airport, the West Valley near Luke Air Force Base and the Goodyear Airport, and areas near Fort Huachuca in Sierra Vista. However, PFAS can also enter water supplies from landfills, wastewater treatment plant effluent, and industrial discharges. If your property is within 5 miles of a military installation, airport, or industrial site, PFAS testing is strongly recommended.

EPA MCLs vs. Health Goals vs. Secondary Standards

Understanding the different types of drinking water standards helps you put your results in the proper context.

Maximum Contaminant Levels (MCLs)

MCLs are legally enforceable standards that apply to public water systems. They represent the maximum concentration of a contaminant allowed in drinking water. MCLs are set as close to the health-based goal as feasible, considering available treatment technology and cost. Private wells are not subject to MCLs, but the standards are the best available benchmark for evaluating water safety.

Maximum Contaminant Level Goals (MCLGs)

MCLGs are non-enforceable health-based goals set at the level where no known or anticipated adverse health effects occur, with an adequate margin of safety. For carcinogens like lead and arsenic, the MCLG is zero. The MCL is set as close to the MCLG as feasible, but treatment limitations and cost often result in MCLs that are higher than MCLGs.

Secondary Standards (SMCLs)

Secondary standards address aesthetic qualities (taste, odor, color) rather than health risks. They are not enforceable but provide useful guidelines. Parameters with secondary standards include TDS (500 mg/L), chloride (250 mg/L), sulfate (250 mg/L), iron (0.3 mg/L), manganese (0.05 mg/L), and pH (6.5-8.5). Exceeding a secondary standard does not mean the water is unsafe, but it may be unpleasant to drink or cause staining and scaling.

Health Advisory Levels

The EPA issues health advisory levels for contaminants that do not yet have formal MCLs. Health advisories are non-enforceable but provide guidance for water systems and homeowners. They are often precursors to future MCL rulemaking.

What to Do If Your Results Show a Problem

Receiving water test results that exceed a standard can be alarming, but there are clear steps to take for each situation.

Immediate Actions for Acute Health Risks

Some results require immediate action:

• E. coli present: Stop drinking the water immediately. Use bottled water for all drinking, cooking, and tooth brushing. Contact a well contractor or plumber to identify and eliminate the contamination source. Disinfect the system (shock chlorination for wells) and retest before resuming use.
• Nitrate above 10 mg/L with infants in the household: Do not use the water for infant formula preparation. Use bottled water for infants. Adults and older children are at lower risk but treatment is still recommended.
• Lead above 15 ug/L: Flush the tap for at least 30 seconds before each use. Do not use hot tap water for drinking or cooking (hot water leaches more lead). Install a point-of-use filter certified for lead removal. Investigate and address the plumbing source.

Treatment Options for Common Contaminants

Contaminant	Effective Treatment Methods	Approximate Cost
Bacteria (coliform, E. coli)	UV disinfection, chlorination, ozone	$500-$2,000 (UV system installed)
Lead	Point-of-use RO, NSF 53 certified filter	$200-$500 (under-sink)
Arsenic	Arsenic-selective adsorption media, RO	$2,000-$5,000 (point-of-entry)
Nitrate	Ion exchange, RO, distillation	$1,000-$3,000 (point-of-entry)
Fluoride	Activated alumina, RO, bone char	$1,000-$3,000 (point-of-entry)
PFAS	Granular activated carbon, RO	$200-$5,000 (depends on system type)
Hardness	Ion exchange water softener	$1,500-$4,000 (whole house)
High TDS	Reverse osmosis	$200-$500 (under-sink) to $3,000-$6,000 (whole house)

Retesting After Treatment

After installing any treatment system, retesting is essential to verify the system is working as intended. AATLS recommends:

• Testing treated water within 2 weeks of system installation.
• Retesting every 6 to 12 months to verify continued performance.
• Retesting after any maintenance or media replacement on the treatment system.
• Retesting both raw (untreated) and treated water to document the treatment system’s removal efficiency.

When to Retest Without Treatment

Some situations warrant retesting the source water before investing in treatment:

• Borderline results: If a result is just above or just below a standard, natural variation may account for the difference. A second sample provides confirmation.
• Unexpected results: If a result does not match historical data or is inconsistent with the known characteristics of your water supply, a resampling rules out sampling error or laboratory error.
• Positive coliform with negative E. coli: Total coliform positive results can sometimes result from sampling technique issues. Resample with careful attention to sterile technique. If the resample is also positive, investigate the contamination pathway.

Annual Testing Recommendations for Arizona Homeowners

Water quality can change over time due to seasonal variation, changes in groundwater levels, new contamination sources, and aging infrastructure. Regular testing protects your family by catching problems early.

For Homes on Private Wells

The EPA and ADEQ recommend the following testing schedule for private well owners:

• Annually: Total coliform bacteria, E. coli, nitrate, pH, and TDS.
• Every 3 years: Full inorganic chemistry panel including arsenic, fluoride, lead, copper, and hardness.
• As needed: PFAS testing if near military installations or industrial sites. Pesticide testing if near agricultural operations. Any parameter with a history of elevated results should be tested annually.
• After any changes: Retest after well repairs, pump replacement, plumbing modifications, nearby construction or land use changes, or any event that could affect water quality (flooding, nearby chemical spills).

For Homes on Municipal Water

Municipal water is tested and reported by the water utility, but testing at your tap provides additional information:

• Every 2-3 years: Lead and copper (first-draw sample after 6 hours stagnation) to assess your specific plumbing.
• After plumbing work: Retest for lead and copper after any plumbing repairs, fixture replacements, or service line work.
• If concerns arise: Test for any parameter where you notice changes in taste, odor, color, or clarity.

How to Get Your Water Tested with AATLS

AATLS makes water testing straightforward for Arizona homeowners.

Step 1: Choose Your Test

Visit orders.aatls.com to browse our residential water testing packages. If you are not sure what to test for, call us at (928) 985-9399 and our team will recommend the appropriate panel based on your water source, location, and concerns.

Step 2: Collect Your Sample

We provide sampling kits with the correct bottles, preservatives, and step-by-step instructions. For most residential tests, you will collect water from your kitchen tap following a simple procedure. For lead and copper testing, samples must be collected as a first-draw after at least 6 hours of non-use.

Step 3: Submit Your Sample

Deliver your sample to our laboratory at 9030 S Rita Rd, Suite 320, Tucson, AZ 85747 or ship it via overnight courier. Bacteriological samples must be received within 30 hours of collection, so local delivery or same-day courier service is recommended for these tests.

Step 4: Receive and Review Your Results

Standard turnaround is 3 to 5 business days for most parameters. Results are delivered as a formal laboratory report with all analytical data, applicable standards, and quality control information. Our team is available to help you interpret your results and understand what actions, if any, are recommended. Explore our full range of testing services for details on specific analyses.

Why Trust AATLS with Your Water Test

Your water test results are only as reliable as the laboratory that produces them. AATLS provides the accreditation, expertise, and service that Arizona homeowners deserve.

• ISO 17025 accredited: Our results are produced under a rigorous quality management system that is independently audited. View our accreditations.
• CDC ELITE certified: For Legionella testing, we meet the CDC’s highest standard for environmental Legionella isolation.
• Arizona-based: We understand Arizona’s unique water quality challenges and can provide context-specific guidance for your results.
• Veteran-owned: Founded by Dr. Glenn Cherry, Air Force veteran, with a commitment to precision and service. Learn more about us.
• Results you can understand: We do not just deliver numbers. We help you understand what your results mean and what to do about them.