How to Shock a Well, Step by Step

Shocking a well means putting enough disinfectant into the water column to kill the bacteria living in the well, the pressure tank, and the pipes, then flushing it out and proving it worked. Here is the whole job, both ways to do it, and where people go wrong.

Step 1: find out how much water your well holds

Every shock treatment starts with the same number: gallons of standing water. A borehole holds 0.0408 × diameter² gallons per vertical foot, so a 6-inch well with 100 feet of standing water holds about 150 gallons. You need the well's depth, its diameter, and the static water level. Most states recorded all three when the well was drilled, and we can pull your official well record from your address in seconds.

Step 2: pick your disinfectant

The traditional method is chlorine: plain unscented 5.25% bleach or calcium hypochlorite pellets, dosed to reach 100 to 200 ppm of free chlorine per the university extension guides. It kills bacteria, and it is what most contractors reach for. It also loses most of its power above a pH of about 7.5, which is where most well water sits, it burns itself up on dissolved iron before reaching the bacteria, and at shock strength it is corrosive to your pump and fixtures.

The newer method is chlorine dioxide, the disinfectant many municipal water plants use. Our kit ships it as sealed Selectrocide sachets that generate 99.9% pure chlorine dioxide right in the mixing container, dosed at 20 ppm following the manufacturer's published shock guidance. It holds its strength across the pH range of real wells and penetrates the biofilm that chlorine glances off. We wrote up the full comparison in chlorine dioxide vs bleach.

Skip the math. We size the dose to your exact well.

Answer a few questions and we pull your well's dimensions from your state's official well record, then pack a chlorine dioxide kit to those exact numbers from $399. A contractor charges $1,500 to $3,000 for the same cleaning.

Find my well See what's in the kit

Step 3: run the treatment

The shape of the job is the same with either chemistry. Bypass your water softener and any filters. Mix the full dose in a clean container and pour it down the casing. Run a garden hose from an outside spigot back into the casing to recirculate until you can detect disinfectant in the hose water, which washes the casing walls above the water line. Then open each tap in the house one at a time until you detect it there, and shut everything off.

Let it sit under no water use for the full contact time, usually 12 to 24 hours. Wear gloves and eye protection for every step that touches the product, and stay upwind of the open wellhead.

Step 4: flush, then prove it worked

Flush the well from an outside spigot onto ground that drains away from your septic system, your garden, and any surface water, until the residual test shows the disinfectant is gone. Then retest for bacteria one to two weeks later. A shock treatment without a follow-up test is a guess. Our kit includes the residual test, and the printed instructions arrive with your well's own numbers written into each step.

Straight answers

How much bleach does it take to shock a well?

It depends entirely on how much water your well holds. Extension services publish targets of 100 to 200 ppm of free chlorine, and a borehole holds 0.0408 times its diameter in inches squared, in gallons per vertical foot of water. A typical 6-inch well with 100 feet of standing water holds about 150 gallons. Guessing is how people end up with a well that still tests positive, or a week of bleach coming out of every tap.

How long after shocking a well can I drink the water?

Give the treatment its full contact time, usually 12 to 24 hours, then flush outside until the residual test shows the disinfectant is gone. Retest the water for bacteria one to two weeks later, and drink from another source until that test comes back clean.

Can I use pool shock to disinfect my well?

Pool shock is calcium hypochlorite, the same chemical in most well sanitizer packs. It works the same way as bleach and carries the same problems: it loses power in alkaline water, burns itself up on iron, and leaves the biofilm layer largely in place. If you use it, use a product labeled for potable water, never a pool blend with algaecides or clarifiers.

Why did the smell or slime come back a month after shocking?

Because chlorine mostly burns the surface of the biofilm where the bacteria live, and the colony underneath regrows. This is the main reason our kit uses chlorine dioxide instead: it penetrates and strips the biofilm itself, per the manufacturer's published data.

How often should I shock my well?

Shock it after any positive bacteria test, after work on the pump or casing, after a flood, or when slime and odor show up. Test the water at least once a year, and let the test results, not the calendar, tell you when to treat.

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