Water · Water Testing
Field test kits detect coliform bacteria as an indicator of contamination. They are useful screening tools. They are not lab tests. Here is what they can and cannot tell you.
The basics
Bacteria water test kits sold for home use are coliform presence/absence tests. They detect whether coliform bacteria are present in a water sample. Coliform bacteria are used by the EPA as an indicator organism — their presence signals that a contamination pathway exists, meaning pathogens could have entered the water supply through the same route.
A positive coliform result means: take action. Per EPA guidance, there is no safe level of coliform in a private well. The specific pathogen involved does not change this. A positive result means stop drinking the water, contact your health department, and address the contamination source.
A negative result means: coliform was not detected at the kit's sensitivity threshold. It does not mean the water is free of viruses, chemical contaminants, heavy metals, nitrates, or any other hazard. Field test kits are screening tools for one category of contamination. They are not a comprehensive safety check.
The most important limitation of field kits over certified lab tests: false negatives. Lab tests are more sensitive, use larger sample volumes, and are performed under controlled conditions. A field kit may miss low-level contamination that a lab would detect. For annual well testing or any situation involving a health concern, use a certified lab, not a field kit.
How many to stock
The EPA and CDC recommend testing private wells at minimum once per year. Stock enough test kits or lab test supplies to support annual testing, plus extra for post-flooding or post-repair checks. Field kits are appropriate for quick screening between annual lab tests — not as replacements for them.
| Scenario | Test type | Stock recommendation |
|---|---|---|
| Annual well test | Certified lab (mail-in) | 1 kit per year per well |
| Post-flooding quick check | Field kit (screen first) | 2–3 field kits per well |
| Stored water before use | Field kit (screening) | 2–4 kits in emergency supply |
| Municipal tap after advisory | Field kit + follow official guidance | 1–2 kits |
Storage
Bacteria test kits use growth media — nutrient broth that supports bacterial growth during incubation. This media has a shelf life, typically 1 to 2 years. Expired media may produce false negatives: the bacteria are present but the media cannot support the growth needed to trigger a color change.
Store kits at room temperature, away from direct sunlight and extreme heat. Many kits include incubation instructions that require holding the sample at body temperature (around 35°C / 95°F) for 24 to 48 hours. A chest pocket works for field incubation; a warm water bath or cooler with a thermometer works at home.
Check expiration dates when you rotate your emergency supplies. An expired bacteria test kit in your emergency bag provides false security. Replace on the same schedule as your water treatment consumables — annually is a reasonable baseline.
Field kits vs. lab tests
The right test depends on your situation. Field kits provide a quick screen. Lab tests provide a defensible result. Use both, in that order, when a contamination concern arises.
WaterSafe, First Alert, Varify. Presence/absence coliform test. Results in 24–48 hours.
Best for: quick screening between lab tests
SimpleLab Tap Score, National Testing Labs. Results in 5–10 business days.
Best for: annual well testing, confirmed concern
NWS recommendation: Keep 2–3 field test kits (WaterSafe or equivalent) in your emergency supplies for quick post-flooding or post-disruption screening. For your annual well test, use a certified lab. Do not substitute field kits for the annual lab test — sensitivity differences matter for low-level contamination.
Safety guidance
A positive coliform result, whether from a field kit or lab test, requires immediate action. Per CDC and EPA guidance: stop drinking the water and use bottled water or another confirmed safe source for drinking and cooking. Contact your local health department — they can advise on next steps and may offer follow-up testing.
For private wells: shock-chlorinate the well using the procedure from your state health department or the EPA's private well guidance. After treatment, wait 24–48 hours and then retest. Do not return to using the well until two consecutive negative tests confirm the contamination has been cleared.
A negative field kit result after a flooding event is not sufficient to return to drinking well water. Field kits can miss low-level contamination. After any flooding event that may have affected your well, use a certified lab test even if the field kit comes back negative.
Per EPA private well guidance (EPA: Protect Your Home's Water) and CDC well water guidelines (CDC: Guidelines for Testing Well Water). Verified June 2026.
Where to buy
Field screening pick
Coliform presence/absence field kit
Tests for total coliform and E. coli. Results in 48 hours. No lab required. EPA-compliant test method. Good for post-flooding screening and emergency supply checks. Keep 2–3 on hand.
$8 – $15 per test
Search AmazonAnnual well test pick
Certified lab mail-in, coliform + nitrates + more
Certified lab test covering bacteria, nitrates, pH, and additional parameters. Recommended by EPA for annual private well testing. Results in 5–10 business days with a plain-language report.
$30 – $150 depending on panel
Search AmazonAffiliate disclosure: New World Survival earns a small commission on purchases made through links on this page, at no cost to you. We only recommend products we would stock in our own kit.
Related
Testing tells you whether to treat. Treatment tells you how to make the water safe. The pages below connect both sides of the system.