Private well owners are responsible for testing their own water, since the EPA doesn’t regulate or monitor private wells. The agency recommends testing at least once a year for bacteria, nitrates, total dissolved solids, and pH. Beyond that annual check, the timing, scope, and method of testing depend on where you live, what’s near your well, and what your water looks, smells, and tastes like.
What to Test For Every Year
Your baseline annual test should cover four things: total coliform bacteria (which signals that disease-causing organisms may have entered your well), nitrates, total dissolved solids, and pH. Coliform bacteria and nitrates are the two most urgent. Nitrate levels above 10 mg/L are especially dangerous for infants and pregnant women, and bacterial contamination can make anyone sick quickly.
Beyond the basics, many well owners should also screen for arsenic, lead, and hardness minerals. The federal safety limit for arsenic is 0.010 mg/L, and lead shares that same action level. Both are tasteless and odorless at dangerous concentrations, so the only way to know is a lab test. If your home has older plumbing, lead testing is particularly important because the metal leaches from pipes and solder joints into standing water.
PFAS, the group of industrial chemicals sometimes called “forever chemicals,” are an increasing concern for well owners near airports, military bases, manufacturing sites, or areas where firefighting foam has been used. The EPA doesn’t set a standard for PFAS in private wells, but recommends contacting your state health or environmental agency for guidance on testing and certified labs that use EPA-approved methods.
When to Test More Often
Certain situations call for immediate testing rather than waiting for your annual check. Test right away if you notice any change in your water’s color, taste, or smell. Test after flooding, nearby construction, new industrial activity, or any other significant land disturbance near your well. If you replace or repair any part of your well system, test again before drinking the water.
Households with infants, young children, elderly adults, or anyone who is pregnant or nursing should consider testing more frequently than once a year. These groups are more vulnerable to contaminants like nitrates and bacteria at levels that might not affect a healthy adult.
What Your Water Is Telling You
Some contamination is invisible, but your senses can flag problems worth investigating. Here’s what common changes mean:
- Rotten egg smell: Hydrogen sulfide gas occurring naturally in groundwater, or bacteria growing in your hot water heater or drain.
- Metallic taste: Iron or copper leaching from pipes. Less commonly, zinc or manganese.
- Brown, red, or orange water: Iron rust, typically from galvanized or cast iron pipes in the home or the water main.
- Blue or green water: Copper corrosion in your plumbing. If dripping water leaves bluish-green stains on porcelain, copper and possibly lead are leaching into your supply.
- Salty taste: Elevated sodium, magnesium, or potassium. In coastal areas, seawater intrusion into the aquifer is a possibility.
- Gasoline or solvent smell: A leaking underground storage tank may be contaminating your groundwater. This warrants urgent testing.
- Cloudy or milky white water: Usually just tiny air bubbles, which clear on their own and aren’t a health concern.
None of these signs replace a lab test. Clear, odorless water can still contain arsenic, lead, nitrates, or bacteria. But sensory changes help you decide what additional contaminants to screen for beyond the standard panel.
Finding a Certified Lab
Use a state-certified drinking water laboratory. Each state runs its own certification program under the Safe Drinking Water Act, and the EPA maintains a directory of contacts for every state’s program. Your local health department can also point you to certified labs in your area. Avoid uncertified labs or mail-order kits that don’t use EPA-approved testing methods, since the results may not be reliable enough to act on.
When you contact the lab, ask what packages they offer. A basic loan-required package covering bacteria, lead, and nitrates runs around $140 at state labs. A comprehensive homeowner package that adds metals screening, volatile organic compounds, hardness, fluoride, and pesticide screening costs closer to $430. Prices vary by state and lab, but those figures from the Wisconsin State Laboratory of Hygiene (current as of January 2025) give a reasonable benchmark.
How to Collect a Good Sample
A contaminated or improperly collected sample is worse than no test at all, because it gives you false confidence or false alarm. Get your sample bottles directly from the lab that will run the analysis. They’ll come pre-labeled and some may contain chemical preservatives, so don’t rinse them out or swap containers.
Choose a cold water faucet that’s clean and free of attachments like aerators, filters, hose connectors, or swivel heads. Kitchen sinks and bathtub faucets work well because they’re high enough to fit a bottle underneath without the faucet touching the container’s opening. Remove any point-of-use filters before collecting.
Open the faucet and let the water run for two to three minutes before collecting. You’re flushing out water that’s been sitting in the pipes so the sample represents what’s actually coming from your well. Watch for the water temperature to stabilize, which signals that fresh groundwater is flowing. Then reduce the flow so it doesn’t splash off surfaces, and fill your bottles according to the lab’s instructions.
Label everything: your name, the date and time, the collection location, and the type of analysis requested. Get the samples to the lab as quickly as possible. Bacteria samples in particular have short holding times, and delays can skew results. Most labs want samples delivered or shipped within 24 to 30 hours of collection, kept cool but not frozen.
Reading Your Results
Your lab report will list each contaminant alongside a reference value. For the key contaminants, these are the numbers that matter:
- Total coliform bacteria: Should be absent (zero). Any positive result means your well may be contaminated with surface water or sewage.
- Nitrates: Below 10 mg/L (measured as nitrogen).
- Arsenic: Below 0.010 mg/L.
- Lead: Below 0.010 mg/L.
If your water exceeds any of these limits, don’t drink it until you’ve addressed the problem. For bacterial contamination, the standard fix is shock chlorination, which involves circulating a strong bleach solution through your entire well and plumbing system. After treatment, you retest to confirm the bacteria are gone before using the water for drinking or cooking again.
Shock Chlorination After a Positive Bacteria Test
Shock chlorination uses ordinary unscented household bleach (6% or 8.25% sodium hypochlorite) to kill bacteria throughout your well and plumbing. Use only fresh, unopened bleach manufactured within six months. You’ll also need a garden hose, chlorine test strips, rubber gloves, eye protection, and about five gallons of clean water from a known safe source like a municipal tap.
The process involves mixing a bleach solution, pouring it into the well, then recirculating water with a garden hose back into the well for about 30 minutes until you can smell chlorine and test strips confirm the concentration is at least 50 parts per million. After that, you shut off the pump and let the chlorinated water sit in the system. Once the waiting period is over, you flush the chlorine out through outdoor spigots (never into a septic system in large volumes) and then through indoor faucets.
No one in the household should use the water during disinfection. If you have water treatment devices, softeners, or appliances with filters, bypass them during the process and follow the manufacturer’s instructions for disinfecting them separately. Replace all filters only after a certified lab confirms your water is coliform-free. If you’re uncomfortable working around electricity and water at the wellhead, hire a licensed well contractor to handle it.