Well water testing is the only way to know what’s actually in your private well, since federal safe drinking water rules don’t apply to it. At De Anza Water Conditioning, Inc, we help San Jose, Los Gatos, Campbell, Saratoga, Cupertino, Morgan Hill, and Gilroy homeowners test annually for bacteria and nitrates, screen for local contaminants like arsenic and perchlorate, and choose the right treatment once results are in.
If your home relies on a private well, well water testing isn’t optional homework, it’s the only checkup your water will ever get. We at De Anza Water Conditioning, Inc have spent years helping South Bay families understand exactly what’s flowing through their taps, and one fact surprises almost everyone: no government agency tests, treats, or monitors your well for you. Water contaminants like bacteria, nitrates, arsenic, and lead can all be present in water that looks, tastes, and smells completely normal, which is exactly why regular testing on private wells matters so much across Santa Clara County.
Why Does Well Water Testing Matter So Much for Private Wells?
Well water testing matters because private wells carry all of the responsibility that public water systems share with regulators. The CDC is direct about this: EPA rules that protect public drinking water systems do not apply to privately owned wells, which means well owners are solely responsible for confirming their water is safe. Nationally, roughly one in five sampled private wells has been found to contain at least one chemical contaminant at levels that could affect health, according to CDC’s environmental health surveillance data.
Because groundwater moves through soil affected by septic systems, agricultural runoff, aging plumbing, and nearby land use, every well’s risk profile is a little different. That’s part of why the EPA specifically directs private well owners to test annually rather than rely on assumptions about water quality.
How Often Should You Test Your Well Water?
You should test your well water at least once a year for total coliform bacteria, nitrates, total dissolved solids, and pH, according to both EPA and CDC guidance. Beyond that annual baseline, test immediately after flooding, well repairs, nearby land disturbance, or any noticeable change in taste, color, or smell. Households near agriculture or older septic systems often benefit from more frequent nitrate checks, particularly during and after wet winter months when runoff increases.
- Private wells are not covered by the federal Safe Drinking Water Act, so testing responsibility falls entirely on the homeowner.
- EPA and CDC both recommend annual testing for total coliform bacteria, nitrates, total dissolved solids, and pH at minimum.
- The EPA’s health-based limit for nitrate in drinking water is 10 milligrams per liter, a threshold set to protect infants from methemoglobinemia.
- Nationally, about one in five tested private wells has shown at least one chemical contaminant at a level that could affect health.
- Common well water contaminants beyond bacteria and nitrates include arsenic, lead, fluoride, and, in some South Bay areas, perchlorate.
What Water Contaminants Should Private Well Owners Test For?
Every private well should be screened annually for total coliform bacteria and nitrates at minimum, with broader panels added every few years or whenever circumstances change. Bacteria such as E. coli typically signal that surface water or septic waste has found a path into the well, while nitrates most often trace back to fertilizer, manure, or septic system runoff, posing the greatest risk to infants and pregnant women.
Beyond that baseline, many Bay Area wells warrant testing for arsenic, lead, fluoride, and other inorganic compounds, since geology and local land use both influence what’s present. Santa Clara County’s own well clearance requirements call for testing a full panel of Title 22 inorganics, including arsenic, lead, and fluoride, whenever a new well or spring is brought into service, which gives a useful baseline for existing wells as well.
Well Water Testing Across Silicon Valley and the South Bay
Local conditions shape what your test results are likely to show. The Santa Clara County Department of Environmental Health oversees well construction clearance and water quality review throughout the county, and homeowners in South County communities including Morgan Hill, San Martin, and Gilroy face an additional requirement: wells in this area must be tested for perchlorate given known historical groundwater contamination in the region. Wells drawing from the Coyote Valley and Llagas groundwater subbasins have also shown notably higher rates of coliform bacteria in past district testing, underscoring why annual checks matter most in these areas.
Homeowners with domestic wells in certain Valley Water groundwater benefit zones covering parts of Santa Clara County, including areas near Los Gatos, Saratoga, and Cupertino, may also qualify for free domestic well testing offered directly through Valley Water’s Groundwater Hotline. Whether or not your well qualifies for that program, pairing a certified lab test with a review of your area’s known groundwater concerns is the clearest way to know what’s actually coming out of your tap in San Jose, Campbell, Santa Clara, and surrounding communities.
What Should You Do If Your Well Water Tests Positive for Contaminants?
If your test results show bacteria, nitrates, or other contaminants above safe levels, switch to bottled or another safe water source immediately and contact your local health department or a water treatment professional. Depending on what’s detected, solutions range from shock chlorination and UV disinfection for bacteria to reverse osmosis, activated carbon, or ion exchange systems for chemical contaminants like nitrates, arsenic, or lead. Reviewing your options with our team helps ensure the fix matches what your specific results actually show, rather than guessing at a one-size-fits-all system. Our guide to reverse osmosis water purity systems is a good starting point if dissolved contaminants show up in your results.
Even if your first round of testing comes back clean, it’s worth staying alert to warning signs between annual checks. We break several of these down in our article on the signs you need professional water testing even when your water looks fine, and for a broader look at what else shows up locally, our complete guide to water contaminants in Silicon Valley covers contaminants beyond what a basic well panel screens for.
Frequently Asked Questions About Well Water Testing
How often should I test my private well water?
You should test your private well water at least once a year for total coliform bacteria, nitrates, total dissolved solids, and pH, per EPA and CDC guidance. Test again right away if you notice a change in taste, color, or smell, after flooding or well repairs, or if there’s new land disturbance or development near your well.
Are private wells regulated the same way as city water?
No, private wells are not regulated the same way as city water, since the federal Safe Drinking Water Act only applies to public water systems. This means well owners are personally responsible for testing, maintaining, and treating their own water supply.
What contaminants are most common in Santa Clara County well water?
Bacteria and nitrates are the most commonly tested contaminants in Santa Clara County wells, with arsenic, lead, and fluoride also screened as part of standard inorganic panels. Wells in South County communities like Morgan Hill, San Martin, and Gilroy face an added perchlorate testing requirement due to known regional groundwater contamination.
Can I test my own well water at home?
You can use a home test kit for basic screening of pH, hardness, and total dissolved solids, but bacteria, arsenic, lead, and other trace contaminants require certified laboratory analysis for reliable results. Any test result that will inform a health or treatment decision should come from a state-certified laboratory rather than a home kit alone.
What should I do if my well water tests positive for bacteria or nitrates?
Stop drinking the water and switch to a safe alternative source immediately if your well tests positive for bacteria or nitrates above safe levels. Contact your local health department or a water treatment professional to confirm the results and determine whether disinfection, filtration, or another treatment approach is needed.
Further Reading & References
- CDC – Guidelines for Testing Well Water
- U.S. EPA – Protect Your Home’s Water (Private Wells)
- County of Santa Clara Environmental Health – Well Construction and Water System Clearance
- Valley Water – Free Testing for Domestic Well Owners
At De Anza Water Conditioning, Inc, we’ve helped private well owners across San Jose, Los Gatos, Campbell, Saratoga, Cupertino, Morgan Hill, and Gilroy get clear, accurate well water testing results and practical next steps. If it’s been more than a year since your last test, or you’ve never tested at all, schedule your free well water test with our team and get real answers about your private well.
