About 43 million Americans rely on private wells for drinking water, according to USGS data. Unlike public water systems, private wells have no federal testing requirements. You are the only quality check on your water.
The EPA’s baseline recommendation is to test your well at least once a year. The three contaminants to test every year without exception: total coliform bacteria, E. coli, and nitrates. These three have the most immediate health risk and the greatest potential to change from year to year based on what happens above and around your aquifer.
Why Annual Testing Isn’t Always Enough
Your aquifer is connected to what happens on the surface. Agricultural runoff, nearby construction, a failed septic system, a flood, a drought, all of these can change your water chemistry without any visible sign. Water can look and taste perfectly normal while carrying E. coli or nitrates at levels above EPA limits.
Annual testing catches long-term trends. It won’t catch an acute contamination event that happens three months after your last test.
The Six Situations That Require Immediate Testing
These don’t wait for your annual schedule.
1. After flooding or heavy rain near your well. Surface contamination can enter through the well casing or overland flow. Test within 1-2 weeks after any flood event that submerged or came near your well casing. See the guide to testing your well after a flood for the specific protocol.
2. After new construction or drilling nearby. Vibration and ground disturbance can introduce sediment and shift aquifer pressures. Give it 4-6 weeks for things to settle, then test bacteria and turbidity.
3. After your septic system fails or backs up. E. coli contamination from a septic failure can reach groundwater within days in some soil conditions. Don’t wait for your annual test. Test bacteria immediately.
4. After any change in water appearance, taste, or smell. Cloudy water, a new odor, a metallic taste, or a rotten egg smell are all signals. Get a test before the scheduled annual. Changes in water quality have causes, and some of them matter for health.
5. After a prolonged dry period. Shallow wells can concentrate contaminants as water levels drop. If your water level has dropped noticeably and you’re on a shallow well, test nitrates and bacteria.
6. If someone in the household has unexplained recurring GI illness. Recurrent diarrhea or nausea without an obvious food cause is worth ruling out the well as a source. Waterborne bacteria are often the culprit in cases that look like “stomach bugs.”
What to Test Annually vs. Less Frequently
Every year: bacteria (total coliform, E. coli) and nitrates. These two tests cost $30-60 from a certified lab and cover the two most common and most serious acute contamination risks.
Every 3-5 years: full expanded panel including arsenic, lead, iron, manganese, pH, hardness, VOCs, and pesticides. If you’re near agricultural land, test nitrates and pesticides every year rather than every few years.
Once at baseline (especially for a new well): PFAS if you’re near a military base, airport, or industrial site that used firefighting foam. PFAS doesn’t change year to year, once you have a baseline reading, you can monitor it on a longer cycle.
Keep Records
A single test result is a data point. A comparison across five years is a story about your aquifer.
An upward trend in nitrates tells you something is changing above your well, likely agricultural activity or a failing septic system nearby. A new coliform hit after years of clean tests points to a specific event, not a chronic problem. Records help you interpret results in context instead of reacting to each test in isolation.
Keep copies of every test result. Email them to yourself with the date and lab name. They matter when you sell the property too, many lenders require water testing documentation at closing.
The Practical Schedule
Mark your calendar now. Annual well testing takes about 20 minutes to collect the sample and costs $30-100 depending on what you’re testing for. For the first test or any test after a gap, include bacteria, nitrates, arsenic, lead, and iron at minimum.
After that: bacteria and nitrates every year, full panel every 3 years. If you’ve never tested and you’ve been on the well for years, start with bacteria and nitrates this week. Then build to the full panel at your next scheduled test.
The well water testing guide covers how to find a certified lab and how to collect samples correctly. For mail-in options, see the best mail-in water tests review.