Well Water Chlorination
Well Water Chlorination and Shock Disinfection
A positive coliform result is common, fixable, and frequently mis-handled. Chlorinating a well is the easy part. Finding out how the bacteria got in is the part that matters.
Shock chlorination is a measured dose of chlorine introduced into the well and circulated through the casing and the household plumbing, held for a period, then flushed out. The household side has to be included — disinfect the well and leave the bacteria in the pipes and you've done half the job.
Why it comes back
Shock chlorination kills what is in the well right now. It does not close the door the bacteria came through. The doors are usually one of these:
- •A cracked, loose or missing well cap, or a cap that isn't vermin-proof.
- •A casing that no longer extends far enough above grade, or is cracked.
- •Surface water running toward the wellhead instead of away from it.
- •A well pit, which lets groundwater and runoff sit against the casing.
- •A failing septic system or a barnyard uphill of the well.
- •Contamination introduced during work on the well — including pump work, which is exactly why we disinfect after we open a system.
If a well tests positive again within weeks of a shock treatment, the answer is not another shock treatment. Something structural needs finding and fixing, and repeat chlorination is money spent to feel better.
After the treatment
Flush until the chlorine is gone. Retest — through a New Jersey certified laboratory — after the chlorine has cleared, not while it's still in there. Retesting is NJDEP's own advice. We don't state a waiting period in days here, because it depends on the well and the dose; we tell you when to sample for the specific job.
When shocking isn't the right answer
Continuous disinfection exists for wells with persistent bacteria. Continuous chlorine injection with a contact tank treats water that a one-time shock can't keep up with and leaves a residual through the plumbing. Ultraviolet treatment handles clear water at the point of entry with no chemical and no residual. Each suits a different problem. See our UV disinfection page for how that one works. We won't price either until we know which you need.
Things people do that make it worse
- •Dumping household bleach down the casing by the gallon.
- •Chlorinating without flushing the plumbing.
- •Chlorinating a well with a softener or carbon filter in line without bypassing it first.
- •Sampling while chlorine is still present and believing the clean result.
Drilling a new well and sealing an old one are a different licence — a licensed well driller — and we don't do that work. See our NJ pump installer licence page.
Straight answers
Questions we get on this one
Can I drink the water during treatment?
No. While chlorine is in the system the water is not for drinking or bathing. You flush it out of the well and every fixture first, then retest through a certified lab before the water goes back to normal use.
Is the chlorine smell dangerous?
The smell means chlorine is still present, which is exactly why you don't drink it yet. Once the system is flushed and the chlorine is gone, the smell goes with it. A lingering smell usually means the flush isn't finished.
Will chlorine hurt my septic system?
A properly dosed shock treatment, flushed through the plumbing and run to the drain in normal amounts, is not a threat to a healthy septic system. Dumping straight bleach by the gallon is a different story, and we don't do that.
Does it damage a softener or a UV lamp?
Chlorine can damage softener resin and carbon filters, and a high dose isn't good for a UV quartz sleeve. That's why treatment equipment gets bypassed before a shock treatment and brought back online after the chlorine is flushed.
My test came back positive but nobody is sick — does it matter?
Yes. Coliform is an indicator, not the illness itself, and a positive result means something is getting into the well that shouldn't be. People drink it for years without symptoms and that doesn't make the entry point harmless. Find the cause.
Do you re-chlorinate after pump work?
Any time a well is opened up — a pump pull, a tank swap, a line opened — the right move is to disinfect before it goes back into service. We broke the seal to do the work, so we chlorinate and recommend a retest to confirm.
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