How do you keep a private well safe in an emergency?

Short answer. Test a private well at least once a year for coliform bacteria, nitrates, total dissolved solids and pH ², and again after any flood or repair ²⁴. If floodwater reached the wellhead, do not drink the water ⁵⁸. Have a well contractor shock-chlorinate it, wait at least 7 to 10 days, then retest ¹. Boil water for 1 minute or use another source until results are clear ¹.

Why is a private well more fragile in an emergency?

On a private well, no utility tests your water or warns you when it goes bad. The owner does both jobs. In England and Wales, local authorities do not have to risk-assess or monitor a supply that serves a single untenanted home; they must do it only if the owner or occupier asks ⁶. U.S., Canadian and Irish agencies likewise address their testing advice to the owner ²⁴⁷.

Emergencies hit a well three ways: a power cut stops the pump, a flood pushes surface water into it, and a drought lowers the water level ⁵.

What happens to well water in a power outage?

Health Canada advises against opening taps, showering or flushing toilets during an outage, because these drain the pressure from the system ⁵. If the system loses all its pressure, or no water comes out of the taps, test the water before you use it again ⁵. When the power comes back, run the water for a few minutes and check that any treatment system, such as a filter or UV unit, is working, following the manufacturer's cleaning steps ⁵.

Well households therefore need stored water. The Phaenyx guides on power outages and water per person cover how much to keep. If you power the pump with a generator, read the generator and carbon monoxide guide first.

How often should a private well be tested?

Agencies agree you need routine tests, but they set different schedules:

Canada is the strictest on bacteria: twice a year, against once a year in the U.S. and Ireland ²⁴⁷. Follow your own country's agency.

Families with infants should not skip the nitrate test. The U.S. EPA warns that infants below six months who drink water with high levels of nitrate can become seriously ill and die ³. Boiling does not remove chemicals from water, nitrate included ⁹ (see the water purification guide). If you prepare formula with well water, ask your doctor or public health unit what to use until you have a clean result.

Use an accredited laboratory. Health Canada says only tests done through an accredited lab or your local public health unit are accurate and reliable ⁴. In Ireland, your local authority or an HSE Environmental Health Officer can point you to a lab ⁷.

When else should you test?

Outside the routine schedule, the agencies say to test:

• after flooding ²⁴, heavy rain, a fire or wildfire, a drought, or a long period without use ⁴;
• after you replace or repair any part of the well system ²⁴;
• when the taste, colour or smell of the water changes ²⁴. EPA Ireland calls such a change "a strong indication that contamination has taken place" ⁷;
• when land use near the well changes ²⁴.

What should you do if floodwater reached the wellhead?

Treat the well as contaminated until tests show otherwise.

1. Stop using the water. Health Canada says not to use it for drinking, cooking, bathing, showering or brushing teeth until you know it is safe ⁵. NSW Health warns that floodwater can carry sewage and microorganisms into bores and that the usual treatment may no longer be enough ⁸.
2. Leave the pump off. Wet or damaged equipment can give an electric shock; have a licensed well contractor inspect the well and wiring first ⁵. The CDC says to turn off all electricity to the well area before clearing debris, and to have a qualified electrician, well contractor or pump contractor check the wiring before power is restored ¹. In New South Wales, a licensed electrician must declare the equipment fit for use ⁸.
3. Use a safe source meanwhile. Until the well has been tested, the CDC says to boil the water at a rolling boil for 1 minute or use another water source ¹. See the water purification guide for methods.
4. Shock-chlorinate, following local guidance. The CDC says a well or pump contractor should disinfect the well because of the safety risks ¹. Disinfection uses unscented household liquid bleach, left in the well and plumbing for at least 12 hours ¹. Your local or state health department can advise on the method to use where you live ¹.
5. Retest, then keep checking. Wait at least 7 to 10 days after disinfection before testing, test again within 2 to 4 weeks and again at 3 to 4 months, then check bacteria at least twice a year ¹.

Fuel and chemicals are a separate problem. Water contaminated with fuel or toxic chemicals is not made safe by boiling or disinfection; if it smells of fuel or chemicals, call your local health department and use bottled water ¹. Health Canada also advises testing for chemicals from nearby fuel, pesticide or chemical storage after a flood ⁵. Securing the house itself is covered in the flood preparedness guide.

For a well that floods repeatedly, Health Canada suggests a licensed contractor extend the casing, fit a flood-proof cap or move the well ⁵.

What should you do when a drought lowers the well?

Health Canada advises conserving water, adding a storage tank, reducing the pumping rate and using other sources ⁵. Do not over-pump: it can clog the well with sediment and cause early failure ⁵. If the well loses pressure, test it and shock-disinfect it ⁵. Long-term options are a deeper well, a municipal connection or treated surface water ⁵.

What official agencies recommend

• United States (CDC, EPA): Test yearly, and immediately after flooding nearby or a repair to the well system ²; after a flood, contractor disinfection, then a test 7 to 10 days later ¹. EPA Safe Drinking Water Hotline: 800-426-4791 ¹.
• Canada (Health Canada and provinces): Bacteria every 6 months ⁴; after a flood, pump off until a licensed contractor inspects it ⁵. Your public health unit or provincial drinking water authority can name an accredited lab ⁴.
• United Kingdom (DWI): In England and Wales, the Private Water Supplies (England) Regulations 2016 (amended 2018) and the Private Water Supplies (Wales) Regulations 2017 give local authorities duties to risk-assess and monitor private supplies ⁶. A single untenanted home is covered only if the owner or occupier asks ⁶.
• Ireland (EPA): Bacteria yearly, chemicals every three years ⁷. Your local authority has information on grants for treatment or a new well ⁷.
• Australia (NSW Health): After a flood, private supplies "may not be suitable for drinking" ⁸. Call your local public health unit on 1300 066 055 ⁸.

Frequently asked questions

Can I drink my well water right after the power comes back?

If the system kept its pressure and nothing else happened, Health Canada says to run the water for a few minutes and check your treatment system ⁵. If the system lost all pressure or the taps ran dry, test the water before using it ⁵.

Does boiling make flooded well water safe?

Boiling for 1 minute handles germs while you wait for test results ¹. It does nothing against fuel or chemicals ¹, and boiling does not remove chemicals such as nitrate ⁹. If the water smells of fuel or chemicals, use bottled water and call your health department ¹.

How soon after shock chlorination can I test?

Wait at least 7 to 10 days, once all the chlorine has been flushed out, then test again within 2 to 4 weeks and at 3 to 4 months ¹.

Who tests a private well in the UK?

In England and Wales, the local authority assesses a supply serving one untenanted home only if the owner or occupier asks ⁶. Contact your council.

Water and air where you live

The Phaenyx water pages set out drinking water rules and alerts country by country.

Your Phaenyx plan includes a "Water and air" section that lists the water and air risks for your postcode. The Phaenyx Safe app keeps the action sheets available offline. Build your Phaenyx plan.

Sources

1. Centers for Disease Control and Prevention — How to Disinfect Wells After an Emergency — https://www.cdc.gov/water-emergency/about/how-to-disinfect-wells-after-an-emergency.html (accessed 2026-10-27)
2. U.S. Environmental Protection Agency — Protect Your Home's Water — https://www.epa.gov/privatewells/protect-your-homes-water (accessed 2026-10-27)
3. U.S. Environmental Protection Agency — Potential Well Water Contaminants and Their Impacts — https://www.epa.gov/privatewells/potential-well-water-contaminants-and-their-impacts (accessed 2026-10-27)
4. Health Canada — Well water and health: Test your well water — https://www.canada.ca/en/health-canada/services/environment/drinking-water/well/test.html (accessed 2026-10-27)
5. Health Canada — Well water and health: Well safety during and after emergencies — https://www.canada.ca/en/health-canada/services/environment/drinking-water/well/safety-during-after-emergencies.html (accessed 2026-10-27)
6. Drinking Water Inspectorate — Roles and responsibilities (private water supplies) — https://www.dwi.gov.uk/private-water-supplies/what-are-private-supplies/pws-roles-responsibilities/ (accessed 2026-10-27)
7. Environmental Protection Agency (Ireland) — Take action on drinking water — https://www.epa.ie/take-action/in-the-home/drinking-water/ (accessed 2026-10-27)
8. NSW Health — Private water supplies after floods or storms — https://www.health.nsw.gov.au/emergency_preparedness/weather/Pages/private-water-supplies.aspx (accessed 2026-10-27)
9. Centers for Disease Control and Prevention — Guidelines for Treating Well Water — https://www.cdc.gov/drinking-water/safety/guidelines-for-treating-well-water.html (accessed 2026-10-27)