Water Wells
Well Disinfection & Testing

Is water from a well safe to drink?

Well water is perhaps the safest form of drinking water available on earth. This is because most drilled wells allow us to tap water that is deep within the protective confines of the earth and has been sheltered from most man made contaminates. This is not to say that every private water well will yield safe drinking water. So the best way to insure water safety is have it tested at a certified laboratory.

How often should I test my water?

If you get your water from a private source, periodic testing of the water for potentially harmful constituents such as bacteria, nitrates or heavy metals will determine whether or not your water is safe for consumption. Most health agencies recommend having your water tested at least annually however it is advisable to increase the frequency of testing if you notice any changes in the aesthetic quality of your water (for example; odor, taste, clarity, etc.). Also, have your water tested if you have had any work done in or around the well such as replacing or servicing the pump and/or drop pipe as this activity can introduce bacteria into the well.

My water test failed. Do I have to install a treatment system?

Probably not! If you had your water tested at a Licensed and Certified Laboratory, and the results came back positive for Coliform Bacteria, AND you have a drilled water well, the well may just need to be "shocked" and re-tested. If the water test showed the presence of E-Coli bacteria, it is advisable to have the well inspected by a N.Y.S. Registered Water Well Contractor or Certified Water Specialist for a source of contamination. If the water comes from a spring or dug well , water treatment with an approved disinfection system is recommended due to the fact that dug wells and springs are difficult if not impossible to protect from surface contamination.

What is Well Shocking?

Well shocking is the process of disinfecting a water well to kill unwanted micro-organisms that have entered the well and may contaminate your drinking water. Shocking a water well may also protect the integrity of the well itself from premature failure due to slime forming bacteria such as Iron or Sulfate Reducing Bacteria.

How Do I Shock My Well?

There is a right way and a wrong way to shock a well. To shock a well correctly, it is important to first understand the process of chlorination and how it affects the well . The purpose of chlorinating the water well is to create a powerful chlorine residual of "free available chlorine" or Hypochlorous Acid and/or Hypochlorite Ion in the water. Bacteria are not killed just by adding chlorine to the water. The chlorine must be added to the breakpoint level at which all oxidizeable substances have been oxidized so that they no longer place a demand on the chlorine. At this point, a free available chlorine residual has been attained and the further addition of chlorine will yield an increased level of free available chlorine to disinfect.

This may all sound complicated, but it’s really not that difficult. The idea is to kill bacteria in the well itself so that a retest of the water will determine if the bacteria are in the aquifer "water supply" or have just found their way into the casing from above.

To properly shock a water well, it is helpful to know the depth of the well along with the well’s recovery rate. The higher the recovery rate, the easier it is to purge the well of sediment, debris and chlorine without fear of running the well dry and potentially damaging the pump or the well itself.

What you will need to shock your well:

  1. Garden hoses long enough to reach the well from an outside spigot.
  2. 5 Gallons of unscented 5.25 percent chlorine household bleach or at least 2 gallons of 12 percent full strength pool type chlorine. Why so much chlorine? These are estimated amounts but vary depending on the depth of your well, the amount of water in it, the recovery rate and more importantly…the chlorine demand of the water. If you are unsure of the exact amount of chlorine you will need, it is better to have more than you need than not enough.
  3. A white 5 gallon bucket.
  4. Pool type Chlorine Test Kit.

These kits can be helpful because despite what you may have heard, you can’t smell "free available chlorine"! What you can smell is Chloramine or Combined Chlorine. Chloramine and Combined Chlorine are formed when you chlorinate water but they have limited disinfection capabilities. What we are after is free available chlorine otherwise known as Hypochlorous Acid which you can not smell!

Hopefully the well isn’t a mile away from the house and you have enough hose to reach the well! If so, you are ready to get started. Pick a good time to shock the well because the water quality may be very poor for a few days after you shock it. The turbulence and chlorine may loosen up and free loads of iron, metalic sulfide and silt from the well and this will pretty much guarantee some ruined laundry if it is done within a few days of the shocking program.

Steps to shock a well:

  1. Let’s get started with bypassing any water filters, softeners or other water treatment equipment that may get plugged by sediment or ruined by high chlorine doses.
  2. Connect garden hose to house and place other end inside the water well. Turn on spigot and let water run back to well for approx. 30 minutes.
  3. After 30 minutes of running water down well, remove hose and run some water into your bucket and note changes in color or clarity. The water may be turbid from sediment that was rinsed from casing. If this is so, run water from hose away from well for 20 minutes or so. This will reduce the chlorine demand of the water by minimizing the turbidity in the well.
  4. Add ½ a gallon of full strength chlorine or 1 gallon bleach into empty bucket and then add a couple of gallons of water from hose into the bucket. Pour this solution down the well and replace the hose end into well. Allow water to run down well for approx. 30 more minutes.
  5. Remove hose and run water into bucket. Note color, odor and clarity of the water. If the water appears highly turbid or smells of strong chlorine, test the water with your chlorine test kit. The color of the water in vial should be "blood red" after you add the OTO drops per instructions on the test kit. If this is the case, turn off the water spigot and let the well stand 12-24 hrs with minimal use. If not, repeat step # 4 until the residual is established. Special Note: If possible, now would be a good time to add a couple hundred gallons of chlorinated water into the well to force the disinfected water back into the formation! This is a trick I have been using for several years and is particularly effective when you are dealing with Iron bacteria.
  6. Now that this shocking dose of chlorine has had at least 12 hours to do its work, turn on garden hose to approx. 2 gallons per minute. You can use your bucket and a watch to establish this flow. Run the hose away from the well to a place where the strong chlorine will not damage gardens or other environments and allow water to run for several hours. Check the water flow every 15 or so minutes to insure that the well hasn’t run dry. If this happens be sure to shut off pump power supply!
  7. With your test kit, check chlorine residual every ½ to 1 hour. When the Free Chlorine residual drops to approx. 5.0 PPM , shut off hose.
  8. Go inside house and place water treatment equipment except carbon filters back into service.
  9. Run water slowly through all hot water faucets until a chlorine residual is established with your test kit.
  10. Now run water through all the cold faucets until a chlorine residual is established. Don’t forget outside faucets, laundry tubs and washing machines. Flush all toilets.
  11. Let water stand in pipes for several hours. The longer the better!
  12. After allowing the water to stand in pipes for several hours, the water can now be used for normal activities but delay your laundry until the water runs clear on hot and cold faucets and is free of chlorine. Note: This may take several days depending on chlorine demand, depth of well, volume of water in the well and recovery rate of well.
  13. Water can be re-tested for potability 1 day after chlorine residual is no longer detected with your test kit.
  14. If the water test passes and the water is potable, it is wise to retest in a month or so to be sure that the bacteria have not returned.

Note: Some wells are very difficult to shock and may take several days to clear after shocking procedure.

If the water fails a bacteria test after this shocking procedure has been performed, it is advisable to have a Certified Water Specialist or NYS Certified Water Well Contractor inspect the well for potential sources of contamination or to make recommendations.

Click here for Coliform and E.Coli Bacteria information.

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