Should You Chlorinate Your Well? When and How to Properly Shock a Well

Every private well will eventually need to be shocked. The question is not if, but when—and whether you should do it yourself or call a professional before the situation turns into an expensive nightmare.

Shocking a well means introducing a strong chlorine solution into the entire water system to kill iron bacteria, sulfur-reducing bacteria, coliform, and other nuisance or pathogenic organisms that quietly colonize the borehole, casing, and plumbing. Homeowners often reach for the bleach bottle after noticing slimy red or black buildup in toilet tanks, rotten-egg odors, cloudy water, or—worst of all—a positive coliform test on a lab report. Those are symptoms, not the root decision point. The smarter approach is understanding the four distinct scenarios that legitimately call for chlorination, and then executing the process correctly so you eliminate the problem instead of merely angering it.

Scenario 1: After Construction, Drilling, or Pump Service

Any time the well is opened—new drilling, hydro-fracturing, pump replacement, or even a simple pressure-switch repair—outside air, tools, and hands introduce contaminants. Bacteria that were never a problem at 150 feet below ground suddenly have a free ride on the casing wall. Every single well professional knows this, yet many homeowners are never told. Best practice is to shock the well the same week service is completed, before the system is put back into daily use.

Scenario 2: Positive Coliform or E. coli Test

A single “present” result for total coliform demands immediate action. E. coli or fecal coliform triggers emergency status. Chlorination is the fastest, least expensive way to disinfect the system while you investigate and repair the source of contamination (cracked casing, bad grout seal, nearby septic leach field, etc.). One successful shock followed by two consecutive “absent” lab tests is usually enough to clear the violation with your county health department.

Scenario 3: Recurring Iron Bacteria or Sulfur Odor

Iron bacteria don’t make you sick, but they create thick biofilm that clogs pipes, stains fixtures, and feeds sulfur-reducing bacteria that produce hydrogen sulfide gas. If you have to clean the red slime out of toilet tanks every few months or the rotten-egg smell comes and goes, periodic shocking—typically once or twice a year—becomes part of responsible well ownership.

Scenario 4: Long Periods of Inactivity

Wells that sit unused for weeks or months (vacation homes, seasonal cabins) turn into perfect incubators. Stagnant water loses its residual chlorine from previous shocks and lets bacteria rebound. A preventative shock before you reopen the house for the season is cheap insurance.

When NOT to Shock

Chlorinating will not fix bad-tasting water caused by minerals, tannins, methane, or high iron levels that are simply dissolved in the aquifer. It will not remove years of iron buildup inside pipes (that requires mechanical cleaning or replacement). And it will not compensate for physical defects like a failing sanitary seal or surface runoff entering the casing. If you shock repeatedly and the problem returns within weeks, you are treating a symptom while the actual pathway for contamination remains open.

How to Properly Shock a Well – Step by Step

Materials you will need:

• Unscented 5.25–8.25% sodium hypochlorite bleach (no splash-less or scented varieties) or calcium hypochlorite granules/pellets sold specifically for well disinfection.

• A clean 5-gallon bucket.

• Garden hose long enough to reach from an outside sillcock back to the wellhead.

• Funnel and a way to bypass or remove the well cap safely.

Step 1 – Calculate the volume Multiply the depth of water in the well (from static level to bottom) by the casing diameter factor:

• 6-inch casing: 1.5 gallons per foot

• 8-inch casing: 2.6 gallons per foot Add 100–200 gallons for the pump, drop pipe, and household plumbing. Example: 200 ft of water in a 6-inch casing = 300 gallons in the borehole + 150 gallons in plumbing = 450 gallons total.

Step 2 – Mix the correct chlorine dose For routine disinfection: 100–200 ppm (parts per million). For heavy bacterial contamination or new construction: 500 ppm. Practical bleach volumes at 6% strength:

• 3 cups (one standard laundry bottle) for every 100 gallons at 100 ppm

• 6 cups per 100 gallons at 200 ppm

• 1 gallon per 100 gallons at 500 ppm

Step 3 – Introduce the solution Remove the well cap or vented sanitary seal. Pour the pre-mixed chlorine directly down the casing, washing the walls as you go (attach a hose to a downstream sillcock, turn it on, and run it back into the well for 10–15 minutes to mix thoroughly).

Step 4 – Surge and circulate Open every faucet in the house—hot and cold—until you smell strong chlorine, then shut them off. This pushes chlorinated water into all plumbing lines and fixtures. Let the solution sit for a minimum of 12 hours, preferably 24 hours. Do not use water for drinking, cooking, showering, or laundry during this time (the Well Harvester® and similar large atmospheric storage systems are a huge advantage here because hundreds of gallons remain available for household use while the actual well is offline).

Step 5 – Flush thoroughly After the contact period, run an outside hose full-blast away from grass, septic fields, and surface water until the chlorine odor is completely gone—often 500–2,000 gallons depending on starting concentration. Test the water with a pool test strip to confirm free chlorine is below 1 ppm before resuming normal use.

Step 6 – Retest Wait at least 7–10 days, then submit a follow-up bacteria sample to a certified lab. Two consecutive “absent” results confirm success.

Safety Notes Worth Repeating

Concentrated chlorine solutions are corrosive and release fumes. Wear gloves, eye protection, and old clothes. Never mix bleach with acids or ammonia-containing cleaners. If you have a constant-pressure system or complex controls, consult your installer first—some variable-frequency drives need to be temporarily bypassed.

The Storage Advantage in Disinfection

Homeowners with low-yield wells or shared well agreements used to dread shocking because the process could leave them without usable water for an entire day or more. Modern atmospheric storage solutions like the Well Harvester® change that equation completely. By harvesting and storing hundreds of gallons in FDA-approved tanks ahead of time, families maintain normal pressure and flow for showers, laundry, and cooking while the actual well sits in 500 ppm chlorine for 24 hours. The booster pump delivers treated, stored water exactly when you need it, turning what used to be a disruptive ordeal into a minor inconvenience.

Final Thought

Shocking your well is not optional maintenance—it is the single most effective tool you have to protect both your family’s health and the long-term reliability of the system. Done correctly and at the right moment, a $30 gallon of bleach can prevent thousands of dollars in pump repairs, plumbing replacement, or medical bills. Ignore the need, and you risk turning a manageable bacterial colony into a full-blown well failure.

If your last disinfection was more than five years ago—or you’ve never done one at all—schedule it this month. Your well will reward you with cleaner, safer water for years to come.