If your private well is flooded, do not use water from it before:
The floodwaters have receded from the well and plumbing.
You have disinfected the well and your plumbing system.
You have received a lab report confirming that the disinfected water contained no harmful organisms.
This document describes the basics of well disinfection with bleach. You can get more detailed information on the web at , by e-mailing , or by calling TCEQ’s Public Drinking Water Section at 512-239-4691.
Before You Begin
Know the hazards: You will be working with water, electricity and chemicals. Be careful – or hire a plumber!
Have enough good drinking water on hand for at least two days: Make sure you have enough good drinking water for all the drinking, cooking, and bathing you will do while you are disinfecting the well and plumbing.
Plan your time: There are three parts to the process of disinfecting your well and plumbing system (~2-3 hrs), and then you need time for sampling and analysis (~2 days to wait for results).
The last part of the process, sampling the water, is important. To be on the safe side, don’t drink or cook with water from your well until a bacteriological lab confirms that the water is free of harmful germs.
How to Disinfect Your Well and Plumbing System
First, gather the information and materials you will need.
Find out where these are:
The power switch to your well pump
The power to your water heater
The wellhead (also called the pumphouse)
The faucet nearest to the wellhead
If your well is pressurized, the pressure release valve (it might look like a faucet)
The well access plug (it might look like a large bolt)
Gather these materials:
Bleach. Use 1 quart of liquid chlorine bleach per 100 feet of well. You must use the right kind of bleach: all chlorine, with no additives. Don’t use scented or odorless bleach. Don’t use hot tub disinfectants. Look for an NSF seal. A list of approved brands is online at
A wrench that fits the well access plug
A funnel
A garden hose long enough to reach the wellhead from the nearest faucet
Disinfecting the Well
The time needed for this part of the process depends on whether your well is pressurized or not. If your well has a screened vent at the wellhead, or if you have not had to use an air compressor to maintain water pressure, your well probably is not pressurized.
Disinfecting a Pressurized Well
This process takes at least 12 hours:
Turn off the power to the well pump and air compressor.
At the wellhead or pumphouse, find the pressure release valve. Before you open it, be sure that you are in the open and breathing fresh air, not the vented air. The vented air may contain hydrogen sulfide, methane, or other gases that sometimes can build up in wells.
Open the pressure release valve to release all the pressure in the well.
Remove the access plug.
Put the funnel in the opening where you removed the access plug.
Pour in the bleach or calcium hypochlorite. (See Table 1 for the right amount to add.)
Replace the access plug and let the well sit for at least 12 hours. During this waiting period:
Following the manufacturer’s directions, turn off the power to your water heater and drain it.
Drain any other water-storage tanks that are connected to your plumbing system.
If you can, collect at least some of this water (for example, in 5-gallon buckets) to use whenever anyone needs to flush a toilet during the rest of the disinfection process.
Locate a lab that is open and can provide a water-sampling kit to use after the waiting period.
When this 12-hour waiting period is over, turn on the power to your well pump and air compressor.
Disinfecting a Nonpressurized Well
Turn off the power to the pump.
Remove the access plug.
Put the funnel in the opening where you removed the access plug.
Pour in the bleach or calcium hypochlorite. (See Table 1 for the right amount to add.)
Connect the garden hose to the faucet nearest the wellhead.
Turn the power to the pump back on.
Turn on the faucet and run water through the funnel into the well for one hour. By circulating the chlorinated well water, you will expose all fittings and equipment in the well to the chlorine solution and improve the germ-killing action.
During this hour:
Following the manufacturer’s directions, turn off the power to your water heater and drain it.
Drain any other water-storage tanks that are connected to your plumbing system.
If you can, collect at least some of this water (for example, in 5-gallon buckets) to use whenever anyone needs to flush a toilet during the rest of the disinfection process.
Find an open lab that can provide a water-sampling kit now.
After the hour is up, remove the garden hose and funnel and, right away, replace the access plug.
Disinfecting Your Plumbing
To disinfect the rest of your plumbing system, you will fill the pipes with chlorinated water from the well and let everything sit for at least overnight—if you can, let it sit for 24 hours. For the best results, do it this way:
Working away from the well, go to the next available outside faucet. Turn it on, run the water until you can smell the sharp odor of bleach (chlorine), and then turn it off.
Repeat step 1 until you have reached all the outside faucets.
Refill the water heater, but don’t turn the heat on yet.
Refill any water-storage tanks.
Go inside and repeat step 1 on every inside hot and cold faucet.
Flush each toilet once.
If you have a chilled-water line on your refrigerator, run it until you smell the odor of bleach.
Now that your plumbing system is full of chlorinated water, let everything stand at least overnight or, if you can, for 24 hours to kill germs in your plumbing. During this time:
Don’t use this water for drinking, cooking, bathing, washing clothes, or washing dishes.
You can use this water for flushing toilets, or you could use water collected from draining your water heater. If the toilet isn’t clogged, it will flush if you pour in two or three gallons of water from a bucket.
If you have an icemaker, let it run, but throw out all the ice it produces.
Run your dishwasher and your clothes washer through a full cycle while they are empty.
Flushing the Bleach out of the System
After the chlorinated water has stood in your plumbing system for 12 to 24 hours, it has probably done all the germ-killing it can do. It’s time to flush the system. This process will take about the same amount of time it took to fill the system with chlorinated water—perhaps 5 to 10 minutes per faucet, on average:
While you are carrying out the rest of these steps, drain your water heater and any other water-storage tanks connected to your plumbing system.
Starting with the outside faucet farthest from your well, open the faucet and run it until you no longer smell chlorine and the water is clear of any debris or color.
Working your way back toward the well, continue step 2 with each outside faucet. Don’t do any inside faucets until you have finished outside—otherwise, you might flood the septic system.
Repeat step 2 with each inside faucet and flush each toilet once.
If you have a chilled-water line, run it until you no longer smell bleach. Throw out all of this water.
Refill the water heater and any other water-storage tanks.
Following the manufacturer’s directions, turn the power to your water heater back on.
Run at least a rinse cycle on your dishwasher and your washing machine.
Your water should now be safe to use for bathing, washing clothes, and washing dishes, but don’t drink it or use it for cooking yet! Before you do, there’s one more important step: confirming that the water is safe to drink by taking a sample and having it tested.
How to Sample Your Water and Understand the Results
Now that you have disinfected the well and your plumbing system, you need to find out if there are harmful organisms in the water. The water needs to be tested for “coliform bacteria.” If coliform bacteria are present, your water may still contain other, more harmful, organisms, and you should disinfect your well and plumbing again.
There are five steps to getting a valid sample and a meaningful test result:
Contact a lab that is accredited to do drinking water sampling.
Get the right container and form from the lab
Collect the sample
Send the sample to the lab for analysis
Read the lab report and understand the results
The lab that you use will give you detailed instructions on steps 2 through 4. The list of labs that can do the coliform bacteria sampling is on TCEQ’s web site at .

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