If a flood reached your wellhead, or surface water pooled around it, treat your well water as unsafe to drink until a lab test says otherwise. Floodwater carries bacteria, sediment, fuel, livestock waste, and chemicals, and any of it can seep into a well through the cap, the casing, or the ground around it. The well may look fine and the water may run clear, but clear water can still be contaminated. Until you disinfect and confirm a clean test, switch to bottled or boiled water for drinking, cooking, and brushing teeth.
Why a flooded well is unsafe until proven otherwise
Here in the Hill Country, flash flooding is a real hazard. Our rivers and creeks rise fast, and wells in low spots, river valleys, and floodplains near the Guadalupe, Medina, Blanco, and Pedernales are the most exposed. The same thin soils and fractured limestone that make our aquifers productive also give surface water quick paths underground. When a creek jumps its banks and water rises over a wellhead, contaminated runoff can travel straight down the casing or through cracks in an aging cap.
The most common contaminant after a flood is coliform bacteria, including E. coli, which signals that surface water and waste have gotten in. You cannot see, smell, or taste it. That is exactly why testing, not a visual check, is the only way to know your water is safe again.
Water trouble now, or planning ahead? Tell us what your well is doing and we will give you a straight answer and a free quote, often the same day.
Immediate steps after the water recedes
Once it is safe to be around the wellhead and the standing water is gone, work through these steps in order:
- Do not drink it. Use bottled water, or bring tap water to a rolling boil for at least one minute and let it cool. Keep using safe water until you have a clean test result in hand.
- Cut power if anything looks wet or damaged. If the pump, pressure tank, or wiring sat underwater, shut off the breaker and do not run the system until it has been inspected. Submerged electrical equipment is a shock and fire risk.
- Inspect the wellhead and cap. Look for a cracked or loose cap, a damaged or leaning casing, missing bolts, or a vent screen that let water in. Note anything that looks off, since these are the gaps floodwater uses.
- Let sediment settle and clear the lines. If the water is muddy, run an outside hose until it runs clear before you disinfect. Do not push muddy water through your softener, filters, or water heater.
- Shock chlorinate the well. Disinfecting the whole system with chlorine kills bacteria in the well, the lines, and the pressure tank. This is the step that actually makes the system safe again, and it must be done before you test.
How shock chlorination works
Shock chlorination means introducing a strong chlorine solution into the well, circulating it through every fixture, and letting it sit so it can disinfect the entire system. You run each tap until you smell chlorine, then leave the chlorine in the lines for several hours, often overnight, before flushing it all out to waste away from your septic field and garden. Done correctly it reaches the casing, the pump, the pressure tank, the water heater, and every line in the house.
It is straightforward in principle, but the right chlorine amount depends on your well depth and water volume, and too little does nothing while too much can damage equipment. If you would rather not handle chlorine and electrical components after a flood, this is a good time to bring in help. Our team handles disinfection as part of water well repair work and can do it safely in one visit.
Test, then retest before you trust it
After disinfection, flush every trace of chlorine from the system, then wait a few days of normal use and collect a sample for a lab test. Testing before the chlorine clears will give you a false reading. You want at least a bacteria (coliform and E. coli) test, and after a flood it is wise to check for nitrates and anything specific to what washed through your property. Our well water testing guide walks through which tests to ask for and how to read the results.
Plan to retest. One clean result right after disinfection is reassuring, but a second test a couple of weeks later confirms the contamination did not simply return through the same opening. If a test keeps coming back positive, the problem is ongoing and needs to be found and fixed, not just chlorinated again. For lingering taste, odor, or staining issues after the water is bacteriologically safe, our well water treatment guide covers your filtration options.
When to call a professional
Handle the bottled-water switch and a basic wellhead look yourself, but call us when:
- The pump or motor sat underwater, or the system will not prime or hold pressure.
- The cap, casing, or wellhead is cracked, leaning, or visibly damaged.
- Tests stay positive after one or two rounds of shock chlorination.
- You are not comfortable mixing and circulating chlorine, or working near submerged wiring.
A submerged pump may need to be pulled, inspected, and resealed, and a damaged casing or cap has to be repaired so the next storm does not put you right back here.
Stop it from happening next time
The best defense against a flooded well is a wellhead that water cannot get into. That means a casing that extends well above the highest flood line, a tight sanitary cap with an intact vent screen, and ground that slopes away so runoff sheds instead of pooling. We check all of this as part of routine water well maintenance, and for wells in known flood-prone spots we can talk through raising the casing or relocating vulnerable equipment.
If your well took on floodwater and you want it disinfected, inspected, and tested the right way, give us a call and we will prioritize getting your water safe to drink again.