Quick Answer:
If irrigation water has crossed into your household pipes after a valve or backflow device failed, immediately close the irrigation isolation valve to stop the source. Then test the household potable system independently (tap water only, with irrigation off) and contact your water utility or a plumber if you see signs of contamination.
Why This Happens
Irrigation systems and household plumbing sometimes share connections or are close to each other. If a valve fails, a hose is left connected, or a backflow preventer malfunctions, irrigation water can be pushed back into the potable supply. Changes in pressure in the municipal line or a sudden drop in house pressure can cause reverse flow. Two common situations are Backfeeding between fixtures and Reverse flow after city pressure change, both of which allow non-potable water to re-enter drinking lines.
Step-by-Step What to Do
Step 1 — Close the irrigation isolation
- Locate the irrigation isolation valve (often near the meter, the irrigation controller, or where the irrigation line leaves the house).
- Turn the valve fully closed to isolate the irrigation system from the house plumbing. This stops more irrigation water from entering the potable system.
Step 2 — Stop using the supply and protect people
- Do not drink, cook with, or bathe using household water until you confirm it’s safe.
- Use bottled water for drinking and food prep if contamination is suspected.
Step 3 — Test the potable system independently
- With the irrigation isolation closed, run a cold water tap for a minute to clear stagnant water, then check clarity, smell, and taste without using hot water.
- Use a basic home test kit for bacteria or contact your local health department or a certified lab for a coliform/E. coli test—be sure the irrigation is off when they test so they evaluate only the potable system.
Step 4 — Inspect backflow prevention and valves
- Look for obvious damage, loose fittings, or bypasses around the backflow preventer. If you have a backflow assembly, note its location and condition but don’t attempt repairs unless you are qualified.
- Record any unusual pressure changes or noises; these will help a professional diagnose the cause.
Step 5 — Follow advised remediation
- If tests show contamination, follow public health guidance: typically a boil advisory or professional disinfection of the system may be required.
- Repair or replace failed valves/backflow devices and retest the potable water before resuming normal use.
What Not to Do
- Don’t run sprinklers while diagnosing or confirming contamination — that may push more irrigation water into the house supply.
- Don’t disconnect or tamper with a backflow prevention device unless you are trained; incorrect work can make the problem worse.
- Don’t assume the water is safe because it looks clear; some contaminants are not visible or odorless.
When to Call a Professional
- If anyone has symptoms of waterborne illness (nausea, vomiting, diarrhea) after using household water, contact a medical professional and your local health department immediately.
- Call a licensed plumber or backflow technician if you cannot locate or close the irrigation isolation valve, or if the backflow preventer appears damaged.
- Contact your water utility if you suspect the problem came from a city pressure event or if multiple homes on your street are affected.
Safety Notes
- Until testing clears the system, avoid consuming or preparing food with household water. Use bottled water or water known to be safe.
- For confirmed contamination, follow official boil-water or disinfection instructions from your local health authority; do not try strong chemicals or improvised treatments without guidance.
- Keep children and pets away from taps that may dispense contaminated water.
Common Homeowner Questions
- Can sprinkler water legally enter my drinking lines? — No, backflow prevention is required to stop that; if it happens, it’s a failure that needs repair.
- How quickly should I close the irrigation isolation? — Immediately; shutting it off is the fastest way to stop more irrigation water from entering the system.
- Can I test the water myself? — You can do a basic home test, but for reliable results use a certified lab or your local health department.