This section has been prepared to answer questions about contaminated wells and to help rural homeowners to restore their wells to safe operating condition. If you need additional information e-mail our department for advice.

Should a Well be Disinfected?

If a well has been contaminated, it should be thoroughly disinfected before the water is used for drinking or in the kitchen. For example, a well should be disinfected as soon as possible after a flood is over, or after a source of contamination has been removed. Of course, disinfection will kill only the disease germs that are already in the well, not any that come in after the disinfection.

If the well was not properly constructed originally, or was damaged by a flood, it may require repair or rebuilding in addition to disinfection.

Why Should I Disinfect a Well That Has Been Flooded?

Flood waters are dirty waters. They carry disease germs from privies, septic tanks, and sewers, as well as filth and silt.

Can I Disinfect the Well Myself?

Certainly. You can disinfect your own well, if you have a few tools, some household bleach solution, and a knack for do-it-yourself work.

How do I Disinfect a Well?

These are the steps you should follow:

1. Pump water from the well to waste until it looks relatively clean.
2. After the water flowing from the well looks clear, stop the pump.
3. Household bleach may now be added to the well. It may be necessary to lift the pump, but some wells have openings that can be used for this purpose. The bleach should be added between the casing and the suction pipe of the pump. See the table for amount of bleach to be used.
4. Do not operate the pump for 30 minutes. After the 30 minute period, with the taps,  faucets and hydrants open or closed, surge the well by starting and stopping the pump several times.
5. Open every tap, faucet or hydrant in the water piping system, start the pump and let water flow until clean water with a strong smell of chlorine comes out.
6. Stop the pump and close all the taps, faucets and hydrants. Do not operate the pump for 8-12 hours.
7. After a period of 8-12 hours (overnight is usually the most convenient period), open ALL taps, faucets and hydrants start the pump, allowing water to circulate to waste until no chlorine odor is present. (NOTE: if household waste is disposed of to a septic tank, DO NOT open inside taps at this time. Before starting pump open only outside taps, so that waste can be circulated to ground surface. Too large an amount of chlorine such as this my be harmful to the beneficial bacterial processes of the septic tank. In addition, the large volume of water would be a heavy load on the leaching field.)

In Step 3 Above, What Kind of Bleach Should I Use?

You can use any ordinary liquid household bleach, if you make sure that it contains chlorine. Read the label and see that it says the bleach contains 5.25 percent sodium hypochlorite. Clorox, Purex, White Magic, and Sani-Clor are some of the trade names for liquid bleaches sold in grocery stores.

How Much Bleach Should I Use?

The amount of bleach you need depends on the size and depth of the well.
If your well is 100 feet deep or less, you can use the following table to find the amount of bleach needed.

If your well is 100 to 200 feet deep, you will need twice as much as for a well 100 feet deep or less. It won't matter if you use more than the amounts shown above, but be sure you use enough.

Where Can I Get Help if I Have an Unusual Problem in Disinfecting my Well?

Please call our office at 415-473-6907 and we will assist you if you have questions about disinfection of wells that are not answered here.