How often should you test well water?

The short answer is at least once a year, plus whenever something changes. The longer answer is a schedule built around the events that most often affect a private well. Use the checklist below to set yours.

How often should you test well water routinely?

The CDC recommends testing well water at least once every year for total coliform bacteria, nitrates, total dissolved solids and pH, and checking the well every spring for mechanical problems. CDC: Guidelines for Testing Well Water EPA recommends the same annual tests. EPA: Protect Your Home's Water The National Ground Water Association recommends testing at least annually for bacteria, nitrates and any contaminants of local concern. NGWA Well Owner's Guide (2021) [CDC-TEST source note] [EPA-PROTECT source note] [NGWA-GUIDE source note]

When should you test well water outside the annual check?

Sources: CDC: Guidelines for Testing Well Water, EPA: Protect Your Home's Water and NGWA (Wellowner.org): Homeowner's Maintenance Checklist. [CDC-TEST source note] [EPA-PROTECT source note] [NGWA-CHECKLIST source note]

Who should test well water more often?

EPA advises testing more often if young children, older adults, or a pregnant or nursing person live in the home. EPA: Protect Your Home's Water [EPA-PROTECT source note]

Contaminants of local concern

Some contaminants, such as arsenic, uranium or radon, come from the rock around the well and change slowly. Others, such as pesticides or fuel compounds, depend on what happens near the well. Ask your local health or environmental department which contaminants matter in your area and how often to test for them. CDC: Guidelines for Testing Well Water [CDC-TEST source note]

Why a yearly test, and why test after events

Two kinds of risk drive the schedule. Some problems build slowly or come and go: a cracked cap, a failing seal or a nearby source can let bacteria into a well that tested clean last year, and nitrate can rise with land use around the well. A yearly test catches those. Other problems arrive suddenly with an event, such as floodwater over the wellhead or a repair that opens the well, so the test needs to follow the event rather than wait for the calendar.

Coliform bacteria are the core of the bacterial test because they are an easy-to-measure indicator: their presence suggests disease-causing organisms may be reaching the water. The Minnesota Department of Health recommends testing for coliform every year, any time the well or water system is worked on, and whenever the water changes in taste, smell or appearance. Minnesota Department of Health: Bacterial Safety of Well Water [MDH-BACTERIA source note]

How often to test for specific contaminants

Sources: CDC: Guidelines for Testing Well Water and Penn State Extension: Water Well Maintenance and Rehabilitation. Where guidance differs, the more frequent schedule is the cautious choice. [CDC-TEST source note] [PSU-REHAB source note]

If you have treatment equipment

Treatment devices such as softeners, filters or disinfection units need their own checks. Ask the lab whether to sample before treatment (to see the well's raw water), after treatment (to see what you drink), or both. Testing after treatment confirms the equipment is working; testing before it shows whether the well itself is changing. Keep the two kinds of results labeled so you can compare like with like from year to year.

Write your schedule down

Put the annual test on the calendar, and keep a one-page log next to your well records: test date, lab, results, and anything that happened since the last test, such as repairs, floods or a change in the water. The log makes event-driven testing a habit rather than an afterthought, and it gives any contractor or buyer the history they'll ask for.

A simple schedule

• Each spring: core panel, plus a look at the wellhead and cap.
• Every few years, or as advised locally: contaminants of local concern.
• Any time a trigger happens: at least the core panel, and bacteria first after floods or repairs.
• Before buying a home with a well: a full panel; see well inspection cost.

Combine the testing schedule with the rest of your well care in the well maintenance checklist, and use how to read well water test results when the report arrives.