There’s a common assumption among well water users that groundwater is naturally clean — filtered through layers of soil and rock, free from the chemicals added to municipal supplies.
That assumption is wrong often enough to matter.
A U.S. Geological Survey study found that nearly one in four private wells in the United States contains at least one contaminant at levels that exceed health-based standards. The more unsettling fact: most of those contaminants have no color, no taste, and no odor. You can’t detect them by looking at your water, drinking it, or smelling it.
This guide gives you everything you need to test your well water correctly in 2026. If you’re looking for professional drinking water testing, our Drinking Water Testing service provides certified laboratory analysis for homeowners throughout Los Angeles.
Why Private Well Owners Are Responsible for Their Own Water Safety
Public water utilities are regulated under the Safe Drinking Water Act. They test continuously, report results to state and federal agencies, and notify you if a contaminant exceeds allowable limits. Your annual Consumer Confidence Report reflects all of this monitoring.
Private wells receive none of that oversight. The EPA does not regulate private wells. Your state health department may offer guidance and low-cost testing, but they don’t monitor your water on an ongoing basis. The moment water leaves the aquifer and enters your well, its safety is entirely your responsibility.
Sources of contamination that affect private wells include:
- Agricultural runoff — fertilizers and pesticides leaching into groundwater from nearby fields
- Septic systems — yours or a neighbor’s, particularly if aging or inadequately separated from the well
- Geological sources — naturally occurring arsenic, radon, uranium, fluoride, iron, and manganese from rock and soil formations
- Industrial and commercial activity — nearby gas stations, dry cleaners, factories, mining operations, landfills, and military facilities
- Aging well infrastructure — damaged casings, cracked seals, and deteriorating pump components that allow surface water and bacteria to enter
- Old plumbing — lead pump components, galvanized pipes, and brass fittings that leach metals into water
- Climate events — flooding, wildfires, and drought all affect groundwater quality
The only way to know what’s in your well is to test it.
What to Test For: A Tiered Well Water Checklist
Well water testing should be matched to your situation. Here’s a practical tiered approach: what everyone should test annually, what to add based on risk factors, and what to include in a comprehensive panel every few years.
Tier 1: Annual Core Testing — Every Well Owner, Every Year
Total Coliform Bacteria The foundational well water test. Coliform bacteria signal that surface water, animal waste, or other contamination has entered the well system. A positive total coliform result immediately triggers follow-up E. coli testing.
- coli (Escherichia coli) Confirms fecal contamination — from a failing septic system, livestock, or wildlife. Any detection of E. coli in drinking water is a health emergency requiring immediate action: a boil-water advisory, disinfection (shock chlorination), and investigation of the contamination pathway. E. coli causes acute gastrointestinal illness and can be fatal in vulnerable populations.
Nitrates and Nitrites The leading chemical contaminant in rural well water, especially in agricultural regions. Nitrates come from fertilizers, animal manure, and septic system effluent — they seep through soil into groundwater and accumulate over time. Nitrates cause methemoglobinemia (“blue baby syndrome”) in infants under 6 months — a condition that reduces blood’s ability to carry oxygen and can be fatal if not caught quickly. The EPA maximum contaminant level (MCL) is 10 mg/L. Test annually; test immediately if a new infant joins the household.
pH Measures water acidity or alkalinity on a scale of 0–14, with 7 being neutral. The ideal range for drinking water is 6.5–8.5. Water with pH below 6.5 is acidic and corrosive — it actively leaches lead and copper from pipes, pump components, and plumbing fixtures into your drinking water. Even if your well has no lead source, low pH can create one by attacking plumbing materials.
Total Dissolved Solids (TDS) A broad measure of all dissolved substances in water — minerals, salts, metals, and organic compounds. Below 300 mg/L is excellent; 300–600 mg/L is acceptable; above 600 mg/L may affect taste and signal elevated concentrations of specific contaminants; above 1,000 mg/L is generally considered unsuitable for drinking. TDS alone doesn’t tell you what’s dissolved — it’s a screening indicator that guides further testing.
Hardness (Calcium and Magnesium) High hardness isn’t a direct health concern but causes scale buildup in pipes, water heaters, and appliances — reducing efficiency and lifespan. Knowing your hardness level determines whether a water softener is warranted and informs interpretation of other test results.
Tier 2: Location and Risk-Based Testing — Add These Based on Your Situation
Arsenic Naturally occurring in rock and soil across much of the United States — particularly in New England, the Upper Midwest, the Southwest, and parts of the West Coast. Arsenic is a known human carcinogen associated with bladder, lung, and skin cancers with long-term exposure. The EPA MCL is 10 parts per billion (ppb), but research suggests health risks begin at concentrations below the regulatory limit. If you’re in a region with known arsenic presence in groundwater, arsenic testing should be annual, not occasional.
Lead Lead enters well water through pump casings, pressure tanks, household plumbing fixtures, and pipes — particularly in homes built before 1986 when lead solder was banned. There is no safe level of lead exposure. In children under 6, lead causes permanent, irreversible neurological damage. Adults face cardiovascular and kidney effects. If your well equipment, pressure tank, or home plumbing is older, lead testing is not optional.
Iron and Manganese Common in well water in areas with iron-rich soil or bedrock. Iron above 0.3 mg/L causes reddish-brown staining on laundry, sinks, and fixtures and an unpleasant metallic or bitter taste. Manganese above 0.05 mg/L causes black staining; at higher concentrations (above 0.3 mg/L), manganese has been associated with neurological effects — particularly concerning for children. If you have staining, discoloration, or metallic taste, test for iron and manganese first.
Radon A naturally radioactive gas formed from uranium decay in rock and soil. Radon dissolves into groundwater and is released into indoor air when water is used for showering, washing dishes, or running appliances. Well water is a secondary but significant radon exposure pathway, particularly in high-radon geological regions (New England, Appalachia, parts of the Rocky Mountain West). Ingested radon exposure is also associated with gastrointestinal cancer risk. If you live in a known radon zone, test both your indoor air and your well water for radon.
Fluoride At low concentrations (around 0.7 mg/L, the level in fluoridated municipal water), fluoride strengthens tooth enamel. At high concentrations — which occur naturally in some geological formations — fluoride causes dental and skeletal fluorosis. The EPA MCL is 4 mg/L, but the health advisory level is 2 mg/L. Test if you’re in an area with naturally occurring fluoride or if you’re supplementing fluoride for children based on incorrect assumptions about your well water content.
PFAS / PFOA (Per- and Polyfluoroalkyl Substances) “Forever chemicals” that don’t break down in the environment or the human body. PFAS have been found in groundwater near military bases that used AFFF firefighting foam, industrial facilities, landfills, and agricultural land where PFAS-containing biosolids were applied as fertilizer. The EPA established maximum contaminant levels for six PFAS compounds in 2024 — at concentrations measured in parts per trillion, reflecting the severity of health risk. Links include cancer, thyroid disruption, immune system effects, and reproductive harm. If you’re within proximity of any known PFAS site, PFAS testing is warranted.
Volatile Organic Compounds (VOCs) Industrial solvents, gasoline additives (benzene, toluene, xylene), and dry cleaning chemicals can leach from underground storage tanks, spills, and improper disposal into groundwater. If your well is near a gas station, dry cleaner, auto shop, manufacturing facility, or former industrial site — or if any of these were historically present in the area — VOC testing is appropriate.
Pesticides and Herbicides Agricultural chemicals applied to nearby fields — atrazine, glyphosate, chlorpyrifos, and others — can leach through soil into groundwater, particularly after heavy rain. In intensively farmed agricultural areas, annual pesticide and herbicide screening is a reasonable precaution.
Coliform (Fecal) — Extended Panel Beyond standard total coliform and E. coli testing, an extended fecal coliform panel helps characterize the nature and source of any biological contamination detected.
Hydrogen Sulfide The source of the characteristic “rotten egg” odor in some well water. Indicates sulfur-reducing bacteria or naturally occurring sulfur. Not directly dangerous at low concentrations but signals bacterial activity and causes corrosion in plumbing and appliances. Hydrogen sulfide is typically detected on-site (it dissipates during sample shipping) rather than by lab analysis.
Tier 3: Comprehensive Testing — Every 3–5 Years
- Full heavy metals panel — lead, arsenic, cadmium, chromium, mercury, barium, selenium, antimony
- Radioactive substances — radium-226, radium-228, uranium, gross alpha and beta radiation; particularly important in granite-heavy geological zones
- Full VOC panel — 50+ volatile organic compounds
- Full pesticide and herbicide panel
- PFAS panel — 40+ PFAS compounds for comprehensive screening
- Microbiological extended panel — Cryptosporidium, Giardia, and additional pathogens relevant to households with immunocompromised members
How Often to Test: Your Well Water Schedule
| Frequency | What to Test |
| Annually (minimum) | Coliform bacteria, E. coli, nitrates, pH, TDS, hardness |
| Annually in risk areas | Arsenic, lead, iron/manganese, radon, fluoride, PFAS |
| Every 3–5 years | Full heavy metals, VOCs, pesticides, radionuclides, PFAS panel |
| Twice yearly | Shallow wells; households with pregnant women; areas near fracking |
| Immediately | After any trigger event (see section below) |
When in spring is ideal: Testing in early spring — after winter runoff and before summer heat — captures the period when bacterial and nitrate contamination from agricultural activity is most likely to be elevated. If you test only once per year, spring is the right time.
When to Test Outside Your Regular Schedule
These situations require immediate testing — don’t wait for your annual date:
After any flooding. Floodwater carries bacteria, agricultural chemicals, and septic waste toward well casings. A well that appears undamaged can still be compromised. Test for coliform bacteria and nitrates within two weeks of any flooding event that reached within 100 feet of your well.
After well repair, pump replacement, or any work on your well system. Any disturbance to the well casing, pump, pressure tank, or related components can introduce contamination or disturb sediment. Test before resuming normal use after any well service.
When you notice any change in taste, odor, color, or pressure. Don’t dismiss sensory changes as cosmetic. Sudden cloudiness, new odors, color changes, or metallic taste are signals to test immediately.
After a septic system failure. A malfunctioning or overflowing septic system near your well creates a direct pathway for bacterial and nitrate contamination. Test immediately and don’t use the water for drinking or cooking until results confirm safety.
When a new infant joins the household. Test specifically for nitrates before the baby arrives. Consider a precautionary threshold of 5 mg/L for infant water use — lower than the EPA’s 10 mg/L MCL.
After nearby chemical spill, agricultural application, or land disturbance. Heavy equipment operation, excavation, grading, or spills near your property can disrupt soil layers and open pathways for surface contaminants to reach groundwater.
After wildfire in your watershed. Wildfires can contaminate groundwater with benzene, VOCs, and heavy metals from burning structures and vegetation. Test for VOCs and a broader chemical panel if wildfire has occurred in your area.
After earthquake activity. Seismic activity can shift soil, crack well casings, and open new contamination pathways. Test after any significant earthquake.
If household members experience recurring gastrointestinal illness. Unexplained stomach illness — particularly if it follows a pattern among household members — is a signal to test for bacteria immediately.
When purchasing a property with an existing well. Treat any existing well as unverified until you have current test results. Test comprehensively before using the water, regardless of what the seller represents or what previous tests showed.
How to Read Your Test Results
Results from a certified laboratory come as numerical values for each parameter, with comparison to EPA maximum contaminant levels (MCLs) or health advisory levels. Here’s how to interpret the most common findings:
| Contaminant | EPA Standard | What to Do If Exceeded |
| Total Coliform | Any presence triggers follow-up | Retest for E. coli; investigate well integrity |
| E. coli | Zero — any detection is unacceptable | Boil-water advisory immediately; shock chlorinate; identify source |
| Nitrates | 10 mg/L | Alternative water for infants; identify agricultural/septic source |
| Arsenic | 10 ppb | Point-of-use reverse osmosis; evaluate geological source |
| Lead | 15 ppb action level (no safe level) | Stop using for drinking/cooking; identify and replace source |
| pH | 6.5–8.5 ideal | Below 6.5: install neutralizer; test for lead and copper leaching |
| TDS | Below 500 mg/L ideal | Above 1,000 mg/L: RO filtration; investigate cause |
| Iron | 0.3 mg/L (aesthetic) | Iron filter; assess pump and casing |
| Manganese | 0.05 mg/L (aesthetic); 0.3 mg/L (health) | Manganese filter; prioritize if children in household |
| Radon | No federal MCL; EPA proposed 300 pCi/L | Point-of-entry aeration system; consult specialist |
| Fluoride | 4 mg/L MCL; 2 mg/L advisory | RO filtration; reassess any fluoride supplementation |
One critical caution about lab selection: Be wary of “free” water tests offered by water treatment product companies. A free test covering only TDS and hardness is a sales tool — it’s designed to make water appear worse than it is to justify selling you a treatment system. Use an independent, state-certified laboratory with no financial interest in what your results show.
What to Do When Your Well Tests Positive for a Contaminant
Finding a contaminant above acceptable levels isn’t a crisis — it’s information. Here’s the appropriate response by contaminant type:
For bacterial contamination (coliform or E. coli):
- Begin a boil-water precaution immediately for all drinking and cooking water
- Shock chlorinate the well according to EPA or your state health department guidelines
- Have a licensed well contractor inspect the casing, cap, and seals for damage
- Retest after disinfection to confirm clearance
- If bacteria recur, investigate septic system location and proximity
For lead:
- Stop using tap water for drinking and cooking until the source is identified
- Contact a licensed plumber to assess pump, pressure tank, and home plumbing for lead components
- Install a certified point-of-use NSF/ANSI 53 filter rated for lead removal while the source is addressed
- Address and replace lead-containing components; retest after replacement
For arsenic:
- Install a certified point-of-use reverse osmosis (RO) system rated for arsenic removal (NSF/ANSI 58)
- Have the system certified and regularly maintained — filter performance degrades over time
- Retest annually to confirm treatment effectiveness
For nitrates:
- Use certified reverse osmosis or distillation for drinking and cooking water (do not boil — boiling concentrates nitrates)
- If an infant is in the household, use certified bottled water for formula and feeding until the source is addressed
- Investigate nearby septic and agricultural sources; consult your county health department
For PFAS:
- Install a certified NSF/ANSI 58 or 62 reverse osmosis or activated carbon block filter rated for PFAS removal
- Check if your area qualifies for remediation funding under EPA PFAS cleanup programs
- Contact your state environmental agency to report the finding — PFAS contamination may affect neighbors too
Well Maintenance: Reducing Risk Between Tests
Testing reveals problems. Maintenance prevents them.
Inspect the well cap and casing annually. The well cap is the primary barrier preventing surface water, insects, and debris from entering the well. Cracks, gaps, or damaged seals are direct contamination pathways. A properly sealed, undamaged cap is non-negotiable.
Maintain a protective buffer around the well. Keep the area within 50–100 feet of your well free from fuel storage, chemicals, fertilizers, pesticides, animal pens, septic components, and road salt.
Know your septic system’s location and condition. Your septic system should be at least 50–100 feet from your well (state requirements vary). Have the tank pumped every 3–5 years and inspected regularly.
Know your well’s age and depth. The average well lifespan is 30–50 years. Older wells may have been constructed to outdated standards with inadequate casing depth or seal quality. If your well is approaching or past 30 years old, have it professionally assessed. Shallow wells (less than 100 feet deep) are significantly more susceptible to surface contamination than deeper wells.
Keep a maintenance log. Document all test results, maintenance work, repairs, and nearby events (flooding, construction, chemical applications) that could affect your water. This record is valuable for diagnosing problems, selling the property, or making insurance claims.
Watch for pressure and flow changes. Changes in water pressure, flow rate, or pump behavior can signal casing damage, pump wear, or aquifer changes — all of which can affect water quality as well as supply.
DIY Test Kits vs. Certified Laboratory Analysis
A note on DIY well water test kits ($20–$100 at hardware stores):
They’re useful for quick spot checks of pH, chlorine, and hardness. For everything else — bacteria, nitrates, lead, arsenic, PFAS, VOCs, radon — they’re inadequate. Home tests are notoriously difficult to read accurately, can’t identify the majority of health-significant contaminants at relevant concentrations, and provide results that aren’t accepted for insurance, legal, or real estate purposes.
“It’s not possible to accurately DIY-test your drinking water,” says Tasha Stoiber of the Environmental Working Group. The right approach: collect your own water samples following laboratory instructions carefully (contaminating the sample container is one of the most common errors that produces false bacterial positives), and send them to a state-certified lab.
In California, drinking water testing laboratories must be certified by the State Water Resources Control Board (SWRCB). Ask for a lab’s certification number and confirm it covers the specific parameters you need before submitting samples.
The Mold Inspection Canary: Water Testing for Los Angeles Area Homeowners
At The Mold Inspection Canary, we provide certified drinking water testing for homeowners throughout the Los Angeles area and surrounding communities — including properties in semi-rural and rural areas with private wells.
Our testing uses accredited laboratory analysis to screen for bacteria, heavy metals, nitrates, pH, TDS, and additional parameters selected based on your property’s specific risk profile, location, and well history. Results come with clear, plain-language interpretation — not just a table of numbers — and specific guidance on what to do if anything requires attention.
Water quality testing is part of the broader environmental health picture we help homeowners address. Along with Drinking Water Testing, we also provide VOC Testing, Mold Inspection, and Mold Testing services to evaluate the safety of your indoor environment.
If you’re a well owner who hasn’t tested in the past year, or if any of the trigger events in this guide apply to your situation, the right move is to test now.
Call 310-567-1160 or schedule your Drinking Water Testing appointment online to receive fast laboratory results and expert guidance.
Frequently Asked Questions: Well Water Testing
1. What contaminants should I test my well for every year?
At minimum, the EPA recommends testing annually for total coliform bacteria, E. coli, nitrates, and pH. Most certified labs recommend adding TDS and hardness to the annual baseline as well. In areas with agricultural activity, add nitrates to your priority list. In regions with known arsenic in groundwater, add arsenic. If your home has older plumbing or well equipment, add lead. Annual testing should be calibrated to your specific location and risk profile — not just the minimum.
2. How do I find a certified lab to test my well water?
Start with your state health department — many maintain lists of certified drinking water laboratories, and some offer low-cost or free testing for basic parameters. In California, laboratories must be certified by the State Water Resources Control Board (SWRCB). Mail-in options like Tap Score also use certified labs. Avoid free testing offered by water treatment companies — their tests are sales tools, not independent analyses.
3. My well water looks and tastes fine. Do I still need to test it?
Yes, absolutely. This is the most common misconception about well water safety. The majority of serious well water contaminants — coliform bacteria, nitrates, arsenic, lead, radon, PFAS — produce no detectable change in the appearance, taste, or smell of water. A U.S. Geological Survey study found that nearly one in four private wells contains at least one contaminant above health-based standards. Sensory quality tells you nothing about microbiological or chemical safety.
4. What happens if my well tests positive for bacteria?
A positive total coliform result requires immediate follow-up testing for E. coli. If E. coli is confirmed, begin a boil-water precaution for all drinking and cooking water, and don’t use tap water for infant formula. The next step is shock chlorination of the well — a disinfection process using chlorine — followed by a repeat test to confirm clearance. Have a licensed well contractor inspect the casing and cap for damage or gaps that allowed surface contamination to enter. If bacteria recur after disinfection, a more thorough investigation of well integrity and septic system proximity is needed.
5. How much does professional well water testing cost?
A basic annual panel — coliform bacteria, E. coli, nitrates, pH, and TDS — typically costs $50–$150 at a certified laboratory. A more comprehensive panel adding heavy metals (lead, arsenic, iron, manganese) and hardness typically runs $150–$300. A full comprehensive test including PFAS, VOCs, pesticides, and radionuclides can range from $300–$600 or more depending on the parameter panel. Given that a well serves as the primary water supply for your family, annual testing at the basic panel level is among the highest-value health investments available to a homeowner.
6. How do I collect a water sample correctly for lab testing?
Follow your laboratory’s specific instructions exactly — they’ll provide a collection kit and detailed protocols. The key rules that most people miss: don’t touch the inside of the sample container with your bare hands (skin bacteria cause false positive coliform results); collect the sample from a cold water tap without an aerator or filter attached; run the tap for 2–3 minutes before collecting to flush standing water from pipes (unless the lab specifically requests a first-draw sample for lead testing, in which case collect without flushing); and ship the sample to the lab within the timeframe specified — bacterial samples are particularly time-sensitive.
