If your home, farm, or business relies on a private well, you should test the water every year for bacteria and nitrates. In Southern Oregon, arsenic should generally be tested every three to five years. Well owners in Northern California should also establish an annual testing schedule and discuss regional contaminants with their county environmental health department.
That is the short answer. The more practical answer is that your testing frequency should reflect your well, property, surrounding land use, and the people drinking the water.
Some wells require more frequent testing. You should also test immediately after flooding, wildfire damage, well repairs, septic problems, unexplained illness, or a sudden change in the water.
One of the biggest mistakes I see is assuming that clear, cold water must be safe. Some of the most serious groundwater contaminants have no noticeable taste, smell, or color. Testing is the only reliable way to know what is in your water. For all your water well drilling contact Enloe Drilling and Pumps
What Is the Recommended Well-Water Testing Schedule?
For most private wells in Southern Oregon and Northern California, I recommend using the following schedule as a starting point:
- Test for total coliform bacteria and E. coli every year.
- Test for nitrates every year.
- Consider testing pH and total dissolved solids every year to monitor changes in the water.
- Test for arsenic every three to five years, particularly in areas with known naturally occurring arsenic.
- Complete a broader mineral and metals analysis when drilling a new well, purchasing a property, or establishing a baseline for an existing well.
- Test for pesticides, herbicides, fuel-related chemicals, or volatile organic compounds when the property’s location or history creates a specific risk.
- Test treated water regularly to confirm that filtration or treatment equipment is still working.
This is not a one-size-fits-all schedule. A properly constructed deep well on a protected residential property may not face the same risks as a shallow older well located downhill from livestock, agricultural land, or a septic drain field.
Read our latest blog: How often should a private residential well be tested for water quality?
Which Well-Water Tests Should Be Done Every Year?
Your annual test should focus on contaminants that can change relatively quickly. These are usually associated with surface runoff, septic systems, agriculture, livestock, flooding, or damage to the well.
Total Coliform Bacteria
Total coliform bacteria are used as an indicator of possible contamination. A positive result may mean that surface water, soil, insects, or organic material has found a way into the well or plumbing system.
A total coliform result does not automatically prove that the water contains a disease-causing organism. It does tell us that the system may be vulnerable and needs further investigation.
E. coli
E. coli is more concerning because it can indicate contamination from human or animal waste. Possible sources include flooding, livestock runoff, a damaged well cap, an improperly sealed casing, or a nearby septic problem.
E. coli cannot reliably be detected through taste, smell, or appearance. Water that looks completely clean can still be unsafe.
Nitrates and Nitrites
Nitrates and nitrites are especially important on rural properties near farms, livestock, fertilized land, or septic systems. Rain and snowmelt can carry nitrogen compounds through the soil and into groundwater.
High nitrate levels are particularly dangerous for infants under six months old. Pregnant women and other vulnerable household members should also take elevated results seriously and seek guidance from an appropriate medical or public-health professional.
Do not boil water to remove nitrates. Boiling causes some water to evaporate and can concentrate the contaminant.
pH and Total Dissolved Solids
Testing pH helps you determine whether the water is acidic, neutral, or alkaline. Acidic water can corrode plumbing and may contribute to metals entering the water from pipes and fixtures.
Total dissolved solids, commonly called TDS, provide a general measurement of dissolved substances in the water. The result does not identify one particular contaminant, but a significant change can indicate that the water chemistry has shifted and that additional testing may be needed.
How Often Should You Test for Arsenic?
The Oregon Health Authority recommends testing domestic well water for arsenic every three to five years. I also recommend testing a new well and testing when purchasing a property served by a private well.
Arsenic occurs naturally in bedrock and soil. It can enter groundwater without creating an unusual taste, smell, or visible color. This makes it one of the clearest examples of why appearance cannot be used to judge water safety.
If an initial arsenic result is elevated or close to the applicable health guideline, follow the laboratory’s or health authority’s advice about confirmation testing. The Oregon Health Authority advises retesting when an initial result is above 8 parts per billion. Water containing arsenic above the 10 parts-per-billion drinking-water standard should not be used for drinking, cooking, or washing food.
If a treatment system is installed, testing must continue. Oregon guidance recommends testing annually at the faucet used for drinking and every three years at the wellhead.
What Other Contaminants Should Be Tested Every Three to Five Years?
Regional geology and land use should determine the contents of your extended laboratory panel. Instead of attempting to test for every possible contaminant, speak to an accredited laboratory or county environmental health department about risks specific to your property.
Iron and Manganese
Iron and manganese can cause staining, sediment, unpleasant tastes, and discoloration. They may also accumulate inside plumbing, pressure equipment, water heaters, and appliances.
These are often treated as aesthetic or operational concerns, but the actual concentration should be reviewed before selecting any treatment equipment.
Hardness
Hard water can leave scale on fixtures and inside pipes, appliances, and water heaters. Testing allows a water softener to be sized according to the actual mineral concentration rather than guesswork.
Lead and Copper
Lead and copper may come from household plumbing rather than the aquifer itself. Low-pH or corrosive water can increase the risk of metals leaching from pipes, solder, and fixtures.
The correct sampling procedure for lead and copper may differ from the process used for bacteria or nitrates. Ask the laboratory whether it requires a first-draw sample or another specific collection method.
Pesticides and Herbicides
If your well is near an orchard, crop field, livestock operation, or heavily treated agricultural land, discuss pesticide and herbicide testing with the laboratory.
These contaminants are not always included in a standard annual panel. The laboratory needs to know about the property and surrounding activities to recommend the appropriate analysis.
Volatile Organic Compounds
Testing for volatile organic compounds, commonly called VOCs, may be appropriate near fuel tanks, workshops, industrial sites, landfills, chemical spills, or wildfire-damaged water infrastructure.
A basic bacteria and nitrate test will not identify these chemicals. You must request a specific VOC analysis or the panel recommended for the suspected source.
Who Should Test Their Well Water More Frequently?
Annual testing is the minimum routine I recommend for most households. Some properties and households need a stricter schedule because contamination could occur more easily or have more serious consequences.
Households With Infants or Pregnant Women
Test before a baby begins drinking the water or having formula mixed with it. Because infants are particularly vulnerable to nitrates, waiting until the normal annual testing date is not worth the risk.
Households with infants or pregnant women should discuss a more frequent schedule with their healthcare provider and local health authority. Depending on the well’s history and location, this may include bacteria, nitrates, lead, manganese, and other locally relevant contaminants.
Properties Near Farms and Livestock
Properties near fertilized fields, manure storage, livestock areas, or agricultural chemical use may face higher risks from nitrates, bacteria, pesticides, and herbicides.
Testing twice a year may be appropriate for a higher-risk property, particularly after periods of heavy rain or snowmelt. The exact schedule should be based on local conditions rather than an arbitrary calendar date.
Wells Near Septic Systems
A properly designed and maintained septic system should operate without contaminating the well. Risk increases when a system malfunctions, the drain field becomes saturated, or the well and septic system are positioned or constructed incorrectly.
Test immediately after a known septic failure. You should also consider more frequent bacteria and nitrate testing if the well is shallow, older, downhill from the septic area, or has previously tested positive.
Older or Shallow Wells
Older wells may have deteriorated casings, damaged caps, poor seals, or outdated construction. Shallow wells are often more vulnerable to surface activity because contaminants have less soil and rock to travel through before reaching the water.
An older well should be physically inspected as well as tested. A laboratory result tells you what is in the water, but it does not show you the condition of the casing, cap, seal, pump, or pressure equipment.
Wells With Previous Contamination
If a well has previously tested positive for bacteria, nitrates, arsenic, or another contaminant, do not return automatically to the standard testing schedule after one acceptable result.
You may need confirmation testing followed by a shorter monitoring interval. If treatment equipment has been installed, test the treated water regularly to verify performance.
When Should You Test Immediately?
Do not wait for your annual reminder if something happens that could affect the well or aquifer. Certain events require immediate inspection and testing.
After Flooding
If floodwater covers the wellhead or pools around the casing, consider the well potentially contaminated. Floodwater may carry sewage, livestock waste, fuel, pesticides, and debris.
Stop using the water for drinking until the well has been assessed and the required testing has been completed. The well may need inspection, disinfection, flushing, and follow-up testing before it is returned to normal use.
After Heavy Rain or Snowmelt
Heavy rain and snowmelt do not contaminate every well, but they can expose weaknesses in older, shallow, damaged, or poorly sealed systems.
If the water becomes cloudy, develops an odor, contains sediment, or tests positive after seasonal weather, you may have a surface-water entry problem that needs to be corrected.
After a Wildfire
Wildfire damage can affect the wellhead, pump wiring, storage equipment, controls, seals, and plastic water lines. Heat-damaged PVC, HDPE, rubber, and other synthetic materials may introduce VOCs or semi-volatile organic compounds into the system.
A post-wildfire assessment may include:
- Total coliform bacteria and E. coli
- VOCs and semi-volatile organic compounds
- Benzene and other fuel-related compounds
- Heavy metals
- Other local contaminants identified by emergency or environmental authorities
Shock chlorination does not remove chemical contamination from melted plastic, fuel, or industrial products. Damaged components may need to be replaced before the well is flushed and tested.
After Well or Pump Repairs
Test after work that opens or disturbs the well system. This includes pulling a submersible pump, repairing the casing, replacing a well cap, modifying drop pipe, or performing substantial plumbing work connected to the well.
Even careful repair work can introduce bacteria or debris. The system may need to be disinfected and then retested after the correct waiting period.
A minor external adjustment to a pressure switch does not automatically contaminate the well, but any repair that exposes the water system should be assessed carefully.
After a Septic System Failure
A sewage backup, saturated drain field, broken septic line, or other septic malfunction is a reason to test immediately, particularly when the well is nearby or downhill from the affected area.
The initial panel should normally include total coliform bacteria, E. coli, and nitrates. Your county environmental health department may recommend additional testing based on the incident.
When the Water Changes
Schedule testing and a system inspection if you notice:
- A new or unusual taste
- A chemical, rotten egg, fuel, or burned-plastic odor
- Cloudiness or discoloration
- Sand, grit, or sediment
- An oily film
- New staining on fixtures or laundry
- Sputtering faucets
- A sudden pressure reduction
A pressure problem is not proof of contamination. It may be caused by a failing pump, pressure tank, pressure switch, plumbing leak, or declining water level. However, a sudden change is a warning that the entire system needs attention.
When Household Members Become Ill
If people in the household develop recurring diarrhea, vomiting, stomach cramps, or another unexplained illness, stop using the well water for drinking and food preparation until it has been investigated.
These symptoms can have many causes, so seek medical advice as well as arranging water testing. Do not attempt to diagnose an illness based on the water alone.
What the Sutherlin Valley Arsenic Study Teaches Well Owners
A regional arsenic investigation in Douglas County provides a powerful example of why routine testing matters.
In 2008, the Douglas County Health Department asked the Oregon Health Authority’s Environmental Health Assessment Program to investigate potential health risks from arsenic-contaminated wells in the Sutherlin Valley area.
The study tested 127 wells in Sutherlin, Oakland, and Yoncalla. Most had no detectable arsenic, but several wells east of Sutherlin exceeded the 10-parts-per-billion drinking-water standard. A small number of wells in the Nonpareil and Hinkle Creek areas recorded arsenic concentrations above 200 parts per billion.
This does not mean that every well in Douglas County or Southern Oregon contains arsenic. It shows how significantly water quality can differ between properties, even within the same general area.
Arsenic comes from natural deposits in rock and soil. It does not require a chemical spill, failing septic system, or visible pollution source. A property owner can maintain the well carefully and still have naturally occurring arsenic in the groundwater.
That is why I would never recommend using taste, smell, or appearance as a substitute for laboratory testing.
What Does Oregon Law Require During a Property Sale?
Oregon’s Domestic Well Testing Act applies to qualifying sales or exchanges of real estate served by a domestic well. After accepting an offer, the seller is required to have the well water tested for arsenic, nitrates, and total coliform bacteria and to share and report the results as required.
Oregon has specific rules covering sample collection and accredited laboratory analysis for these transactions. Certain types of wells and properties may be exempt, so buyers and sellers should confirm the current requirements with the Oregon Health Authority or an appropriate real-estate professional.
The legal requirement applies to qualifying property transactions, but I do not believe homeowners should wait until they sell before testing. Your family may have consumed the water for years by that stage.
What Is the Best Time of Year to Test Well Water?
The most important step is choosing a consistent date and testing every year. A perfectly selected season does not help if you keep forgetting to arrange the test.
Late spring or early summer can be a useful testing period in Southern Oregon and Northern California. Rain and snowmelt may place more pressure on vulnerable wells and expose problems associated with runoff.
However, you should not wait for spring if the well has flooded, the septic system has failed, the water has changed, or another warning sign has appeared. Event-based testing always takes priority over your normal schedule.
A simple system is to link your annual water test to another household task, such as:
- Cleaning the gutters
- Servicing the heating or cooling system
- Checking smoke detectors
- Preparing irrigation equipment for the season
- Completing annual property maintenance
Add a recurring calendar reminder for your annual bacteria and nitrate test. Create a separate reminder every three to five years for arsenic and your broader mineral panel.
Should You Use a Home Test Kit or a Certified Laboratory?
Home test strips can provide basic screening information, but I would not use them to make an important health, property, or treatment decision.
An accredited laboratory can measure specific contaminant concentrations and provide results that can be compared with recognized health guidelines. This is particularly important for bacteria, nitrates, arsenic, lead, pesticides, and VOCs.
The laboratory will also provide the correct bottles. Different tests may require different containers, preservatives, fill levels, temperatures, and delivery times.
When Homeowners Can Collect the Sample
Homeowners can often collect routine samples if the laboratory allows it and its instructions are followed exactly.
Common sampling mistakes include:
- Using a household bottle instead of the laboratory container
- Touching the inside of the bottle or cap
- Rinsing out a required preservative
- Sampling through a garden hose or treatment system
- Using the wrong faucet
- Collecting a first-draw sample when flushing is required
- Flushing the faucet when a first-draw sample is required
- Delivering the sample after its permitted holding time
Follow the instructions for each individual test. Bacteria, lead, metals, and VOC samples may require different collection methods.
When Professional Collection Is Better
Professional or independent sample collection may be appropriate for:
- Real-estate transactions
- Legal or property disputes
- Insurance matters
- Commercial or regulated water use
- Complex contamination investigations
- Situations requiring documented chain of custody
For an Oregon property transaction, ensure the sample and analysis comply with the applicable Oregon rules.
What Well-Water Records Should You Keep?
Keep every result rather than looking at the latest report in isolation. Historical records can reveal a slow rise in nitrates, changing pH, recurring bacteria, increasing sediment, or declining treatment performance.
Your well file should include:
- The original well log or driller’s report
- Well depth, casing information, and original yield
- All laboratory water-test reports
- Dates and details of bacteria detections
- Shock-chlorination records
- Pump installation and replacement information
- Pressure tank and control-system records
- Filter and treatment-system maintenance
- Well inspections and casing repairs
- Changes to nearby land use or septic systems
A physical binder works well, but I recommend also keeping digital copies. Label every report with the sample date and location, such as “untreated wellhead” or “kitchen faucet after treatment.”
What Should You Do When a Test Finds a Problem?
Do not rush out and buy the first treatment system advertised online. The correct solution depends on the contaminant, concentration, water chemistry, source of the problem, and amount of water your property uses.
A sensible process is:
- Review the result with the laboratory or local health authority.
- Stop using the water for drinking if advised.
- Repeat the test when confirmation is appropriate.
- Inspect the well and pump system for physical defects.
- Investigate septic, agricultural, flood, wildfire, or land-use risks.
- Select repairs or treatment designed for the confirmed problem.
- Retest the water to verify that the solution works.
- Continue monitoring at the recommended interval.
A failed test does not always mean the aquifer is permanently contaminated. Bacteria may enter through a damaged well cap, failed seal, deteriorated casing, or another repairable defect.
Other contaminants, including arsenic or nitrates, may require specialized treatment or a different long-term water solution. Testing gives you the evidence needed to make the correct decision.
How Enloe Drilling and Pumps Can Help
Laboratory testing identifies what is in the water. A professional well and pump inspection helps determine whether the result is connected to a physical system problem.
Enloe Drilling and Pumps provides water well drilling, pump installation, pump repair, water well testing support, yield testing, and system diagnostics throughout Southern Oregon and Northern California.
Our team can inspect components such as the well cap, casing, pump, pressure tank, controls, and associated equipment. If a physical defect is allowing contamination into the system, repairing that defect is often more important than installing another filter.
We also match new pumps to the well’s depth, yield, pumping level, pressure requirements, and expected demand. An oversized pump can withdraw water faster than the well recovers, potentially contributing to sediment, reduced performance, or dry-run damage.
If an aquifer is no longer dependable or a well cannot be rehabilitated economically, a new well may need to be considered. That decision should be based on site conditions, well records, testing, professional inspection, and local regulatory requirements.
Make Well-Water Testing Part of Your Annual Maintenance
For most private well owners, the simplest reliable rule is to test for bacteria and nitrates every year and arsenic every three to five years. Expand the panel according to local geology, surrounding land use, household vulnerability, and previous results.
Test more frequently if your well has a history of contamination, your septic system has malfunctioned, an infant drinks the water, or well equipment has failed. Test immediately after flooding, wildfire damage, major repairs, unexplained illness, or a noticeable change in the water.
Your water does not need to look dirty to contain a problem. A recurring laboratory test is a small maintenance task compared with the health risks, equipment damage, and property complications that can result from years of uncertainty.
If you need help evaluating your well or pump system in Southern Oregon or Northern California, contact Enloe Drilling and Pumps for professional guidance and a site-specific assessment.