Properly constructed private water supply systems require little routine maintenance. These simple steps will help protect your system and investment.
Shock Disinfection of a Well
The purpose of shock disinfection of a well system is to destroy bacterial contamination present in the well system at the time of disinfection and is not intended to kill bacteria that might be introduced at a later time. A well may be contaminated with bacteria due several reasons such as lack of use or from bacteria that has entered the well system from the aquifer or from the surface water contamination.
Another option to remove bacteria contamination from well water is having a plumber install an ultraviolet light (U.V. light) treatment system. UV light treatment systems can be installed in line inside your home in a short time period and require typical bulb replacement and cleaning of lens annually.
Often a 5 micron sediment filter is installed prior to the UV light to keep the lens clean. Cost including installation of filter and UV light is often $700 to $1000. UV lights are recommended if bacteria contamination returns after shock chlorinating a well.
All well caps should be installed 18 inches above grade level or have a water tight sealed cap if the well cap is installed in a pit to deter contamination from surface water. Therefore, it is vital that the well be constructed so that no new contamination may enter the well following completion of the shock disinfection. if any plumbing repairs are performed to your well then it is recommended to shock chlorinate the system after repairs are completed.
In order to achieve a satisfactory disinfection of the system, the bacteria must be brought in contact with a chlorine solution of sufficient strength and remain in contact with that solution for a sufficient time to achieve a complete kill of all bacteria and other microorganisms.
If drinking water has been tested and has not passed standards for safe drinking, or any time the building water supply system has been opened for repairs (such as replacing a submersible well pump or a jet pump foot valve), the well should be disinfected following these procedures, and should be re-tested after well shocking is completed.
If you don't know where the well is located, you'll have to find it before this well chlorination procedure can be best performed. It's possible to get chlorine into the well by sending it through the building piping and pump but that step won't sterilize the interior and sides of the well casing - so the procedure below is a better one.
Pour Clorox™ Bleach (or an equivalent brand of household bleach) which is typically 5% or hypochlorite granules down into the well. Some people use swimming pool chlorine tablets which have the advantage that they sink to and sterilize water at the well bottom, and the disadvantage that it takes longer to flush out the chlorine.
How much bleach to use when shocking a well: Health department officials can give more precise guidance about the amount of disinfectant needed based on the depth of the well. Common well shocking guidelines for the amount of household bleach needed are given in the table just below.
Quantity of Chlorine or Household Bleach Needed to Shock a Well
Well Depth in Feet (6-inch diameter well casing) Volume of standard household bleach needed: Well depth 100' then use 3 cups Clorox or 2 oz. of granules Well depth 200' then use 6 cups Clorox or 4 oz. of granules Well depth 300' then use 9 cups Clorox or 6 oz. of granules Well depth 400' then use 12 cups Clorox or 9 oz. of granule Well depth 500' then use 1 gallon Clorox or 12 oz. of granules
Watch out: NOTE to be accurate in reaching the necessary concentration of chlorine in your well, treat the "depths" listed above as if they were the height of the actual column of water in your well (assuming a standard casing which is 1.5 gallons per foot of height). So if your well is 400 feet deep, but if 100 feet of it is air, your water depth is actually 300 ft. The actual quantity of water in a well bore when the well is at rest is defined as the static head.
To determine the actual well water volume, take the depth of the well minus the depth from top of well shaft down to the water level. This can be measured with a tape measure or drop line. If you are not comfortable measuring or disinfecting the well contact a plumber to perform this task.
Watch out: for inadequate well disinfection: use enough bleach to reach the necessary concentration in the well and let the disinfectant remain in the well long enough (8-24 hours) - otherwise you may fail to adequately disinfect the well.
Watch out: for excessive well disinfection: don't significantly "overdose" the well with bleach or chlorine or you may find that you have to waste a lot of water and time flushing out the chlorine bleach at the end of the disinfection period.
Watch out: for difficult-to-sanitize wells or if the water well has been contaminated by area flooding extra steps and extra safety precautions needed.
Prepare the well, plumbing system, equipment: fix any leaks, inoperative controls, or obvious nearby contaminant sources. Take any charcoal-filter type water treatment equipment offline.
Introduce the chlorine solution into the top of the well. Remove the cap at the upper terminal of the well casing and pour the chlorine solution down the inside of the casing.
If the well casing terminates through the floor of a pump house, then the casing is required to have a well seal at the upper terminal [i.e. at the top of the casing]. This well seal can be loosened and the chlorine solution introduced into the well at that point.
Using a garden hose, spray water down into the well pipe to wash the chlorine solution down to the bottom of the well. Ten to twenty gallons of water should be enough. Running more chlorinated water down the casing sides won't hurt nor risk running the well dry since you're recycling the well water through the plumbing and back to the well. This step in the well shock procedure, by recycling chlorinated water out of the building plumbing and back into the well both cleans the well casing, piping, wiring, and also avoids wasting water.
Watch out: shock hazard: if on opening the well casing you see exposed electrical wires or flimsy electrical connections you should have a qualified electrician or repair person make sound, water-tight splices and coverings before attempting to wash down the well casing interior.
Watch out: disinfecting or shocking a well may also be ineffective if the well casing and sides are coated with mineral deposits or biofilm that form in some water wells. Mechanical cleaning may be necessary to obtain a successful outcome. More aggressive well disinfection procedures may be required.
Turn on all cold-water household taps until you can smell the Clorox coming out of every plumbing fixture water supply, including the faucet farthest from the well.
Watch out: notice that we did not include the water heater system and hot water tank in this step. However, you may wish to also turn off and then drain the water heater to eliminate any possibly contaminated water from that tank before restoring your water system to operation. If you elect to shock (sterilize) the water heater tank interior, we recommend that step be performed with the water heater turned off (don't heat a water-bleach mix) and that the heater be left OFF until the tank has been drained and flushed and then re-filled.
Watch out: Also, heating water that contains a high level of chlorine might produce potentially dangerous chlorine gas coming out of a hot water faucet.
Turn off the water and do not use it for 8 to 24 hours. Seal the top of the well. Do not run laundry with this chlorinated water or it may bleach clothing unexpectedly.
Flush out the Clorox™ (or other brand) bleach solution: at the end of the standing period, operate the well pump (run the water) water until you can no longer smell the Clorox.
Watch out: Do not run Clorox™ into the septic system - run water outside through an outside faucet or hose. There should be a hose connection at the at the bottom of the water pressure tank.
When you no longer smell chlorine at the hose draining the water pressure tank, close off the drain and open all faucets in the house to flush out house piping for fifteen minutes or until you no longer smell or taste chlorine [whichever is longer].
Watch out: if you do not first drain the water pressure tank of chlorinated water it can take a much longer time to flush the bleach smell out of the water supply. And if you have put chlorinated water into the water heater tank, that tank too will best be flushed out. (Be sure the water heater is turned OFF before draining the heater tank or you can damage that system.
Watch out: if you forget to take any charcoal-filter equipment offline before introducing a disinfectant you may find it almost impossible to get the bleach odor out of the system later. You may have to replace activated charcoal or charcoal filters in your water treatment equipment if chlorine or bleach odor remains a problem. You will want to replace such equipment in any event if it was contaminated by floodwaters or other sources.
Watch out: If your well has a limited flow rate or poor recovery rate there is a risk that you may simply run out of water during the flush-out step.
Watch out: if you used a low-odor or "odorless" bleach product to shock the well you may have trouble knowing if you've flushed out all of the bleach product. Leaving bleach in drinking water can be dangerous and of course it could cause some surprises in the laundry too.
We recommend using chlorine test strips to check for residual chlorine after flushing bleach out of a well water system before taking a new water sample to a lab for re-testing. Retest the well water after all the Clorox or chlorine is out of the system and the water has been used for 5-7 days (typical health department guideline) if time permits. The longer you wait until the well water retest the more valid will be the results, because you are giving time for a remaining bacterial contaminating colony to reproduce. Lab testing typically includes testing for a very low level of chlorine so make sure you run water long enough to allow for all residual chlorine to be removed.
Steps to protect from running out of well water during shocking and flushing out a well:
Recycle well casing flush-water: One of the steps in shocking a well, using a garden hose connected to the building to use chlorinated water to wash-down the well casing sides during the initial steps in the well shock procedure will reduce the water consumed, but during the flush-out period a low-yield well may still run out. Empty the water pressure tank (and water heater tank if that was shocked): A second step that may be able to reduce the water wasted trying to flush out the bleach odor from the building water supply after shocking a well (thus also reducing the chances of running out of water) is to completely empty the water pressure tank and the water heater tank, refilling them with fresh water from the well as soon as incoming well water at a close-by tap is low or has no bleach odor.
Install equipment to protect the well pump: A third step to protect a well and pump from "running out of water" is the installation of special low water controls in the well that will recycle water in the pump and reduce or stop well water flowing into the structure should water level in the well drop too low.
Don't leave water running unattended. On occasion when a well has a limited recovery rate, a home owner, or water tester may "forget" to keep track of how long water has been run, simply leaving faucets open without watching for a diminished or stopped water flow.
Any time you are running water to test or service a building that uses a private pump and well system for its water supply, you should continuously monitor the water running out of one or more fixtures. If you see the water flow rate significantly diminish or stop you should immediately turn off the well pump to protect it from damage.
Then try waiting half an hour or more before turning the pump back on. That procedure will also give insight into how quickly a low-flow-rate well will recover.