How often should private well water be tested?A practical calendar for Michigan homeowners.

The EPA and CDC both recommend testing private well water at least once a year for total coliform bacteria, nitrates, total dissolved solids, and pH. Michigan health agencies give similar guidance because private wells can change after heavy rain, nearby construction, septic issues, or changes in groundwater movement.

Think of annual testing as the minimum, not the finish line. A yearly sample tells you whether the well is still behaving like it did last year. It does not prove the water will stay unchanged after a flood, after a well cap is damaged, or after a new odor appears at the kitchen sink.

A good annual screen starts with the indicators that reveal whether the well is sanitary and chemically stable. These are the common baseline tests homeowners should discuss with a qualified water professional or local health department:

• Total coliform bacteria and E. coli: indicators that surface water, septic influence, animals, or damaged well components may be reaching the water supply.
• Nitrate: especially important near farm fields, fertilized lawns, septic systems, or shallow aquifers. Nitrate is a serious concern for infants and pregnant people.
• pH: shows how acidic or basic the water is. Low pH can contribute to corrosion and metal leaching from plumbing.
• Total dissolved solids: a broad indicator of minerals and dissolved material that can affect taste, scaling, and treatment performance.

Many Michigan homeowners also add hardness, iron, manganese, arsenic, lead, copper, chloride, and sulfate depending on location, plumbing age, symptoms, and prior test history. A baseline panel is most useful when it reflects the actual risks around the well.

Do not wait for the annual date if something changes. A private well should be sampled after any event that could introduce contamination or change water chemistry.

• After flooding or heavy runoff: floodwater can carry bacteria, fertilizers, fuel, and septic waste toward the wellhead.
• After well service or pump work: opening the system can introduce bacteria if the well is not disinfected and flushed correctly.
• After a new smell, taste, or color appears: sulfur odor, metallic taste, cloudiness, orange staining, or black staining all deserve a targeted test.
• Before buying a home: a real estate transfer should include current lab results, not old paperwork from the seller.
• When a baby, pregnant person, older adult, or immunocompromised person lives in the home: risk tolerance should be lower.
• If nearby land use changes: new construction, chemical storage, road salt runoff, septic failures, or agricultural changes can affect groundwater.

Michigan well owners should pay attention to both naturally occurring groundwater chemistry and contamination from human activity. Iron and hardness are common aesthetic issues in many southeast Michigan wells. Arsenic is a known concern in parts of Michigan and should be checked when a well is new, newly purchased, or lacking reliable records.

PFAS is another Michigan-specific concern because the state has documented contamination at many sites and maintains active public tracking through EGLE. PFAS testing is not part of every basic annual panel, so homeowners near known sites, industrial activity, airports, military facilities, landfills, or firefighting foam use should ask specifically about it.

Test results become more valuable over time. One nitrate result tells you what happened on one day. Five years of nitrate results show whether the well is stable, trending upward, or responding to nearby changes.

Keep lab reports, treatment equipment manuals, filter change dates, well depth records, pump service history, and any disinfection notes in one folder. If you ever sell the home, troubleshoot a treatment system, or respond to a health concern, that file saves time.

• U.S. EPA: Private Drinking Water Wells
• CDC: About Private Wells
• MDHHS: Care for Mi Drinking Water
• Michigan EGLE: Water Well Construction