Coliform Bacteria in Your Well Water: What Does It Cost to Fix in Maryland?
Angi’s 2026 cost guide puts a professional well shock at $80 to $200. The Well Guide lists a UV system at $200 to $800, plus $150 to $300 to install. Both treat coliform bacteria in well water. Our well chlorination service clears what is already in the system. A repeat positive means the path in is still open.
A lab report showing total coliform or E. coli raises two questions. Is the water safe to use, and what will the fix cost? Health agencies answer the first, and the cost depends on how the bacteria got into the well. One shock chlorination may not hold while that path stays open.
The ranges below are published market data from Angi, The Well Guide and the Frederick County Health Department. HydroWells is based in Poolesville and Dickerson and works on wells in Montgomery, Frederick, Carroll, Howard, Washington and Baltimore County. Your own number comes from a free estimate, written after a look at the property.
What does a positive coliform test mean for your well?
It means the lab found bacteria in your sample. Frederick County’s certificate of potability needs two bacteria samples, both free of total coliforms and E. coli. University of Maryland Extension posts a well disinfection handout with household advice. It says to wait for a negative total coliform test before drinking or cooking with the water.
Your report may list total coliform, E. coli or both. The Minnesota Department of Health calls total coliform a group of indicator bacteria that are everywhere on the surface of the ground but do not usually occur past a few feet into the soil. Most do not cause disease, yet a positive result can indicate that surface contamination has gotten into the water. Ask the lab or your county health department what each line means for your household. Frederick County’s health department also lists times to test beyond the yearly check, such as recurrent stomach problems in the family or a pregnant woman or newborn baby drinking the water.
How do coliform bacteria get into a well?
Bacteria get in with surface water or through an opening in the well. MDE notes that rainwater can pick up harmful bacteria on the land surface. It says a well should sit where that rainwater cannot collect and seep into it. EPA and county sources point to these paths in.
EPA tells owners to inspect the exposed parts of a well from time to time. It also says flooding is a common cause of private well contamination. Frederick County’s health department adds work on the system, from a new well to a pump swap or plumbing repair. MDE says wells in flood-prone areas should be fitted with a flood-proof well cap.
- A broken, missing or loose well cap
- A cracked, corroded or damaged well casing
- Settling or cracking in the surface seal
- Surface water or shallow groundwater flowing into the well
- Structural failure in older, shallow wells
What does it cost to fix coliform bacteria in a well?
It depends on which fix the well needs. A professional shock runs $80 to $200 in Angi’s 2026 guide. The Well Guide puts a UV system at $200 to $800, plus $150 to $300 to install. It puts a replacement well, the last resort, at $8,000 to $20,000.
Angi ties the shock price to well depth, diameter and local labor rates. These are national figures plus one Maryland county’s lab fees, so read them as market data. Wellhead repairs, such as a new sanitary cap or a casing extension, get quoted after a look at the well. Our well water testing cost guide covers lab fees in more detail.
Frederick County says repair or replacement of the well may be required when contamination persists after repeated disinfection. For a well contaminated by a persistent source, The Well Guide says a new well elsewhere is often preferable. Montgomery County’s water and sewer plan lists well disinfection and replacement wells among the fixes for problem wells. Our well drilling cost guide covers that price in Maryland.
Published ranges for the usual coliform fixes
| Fix | When it fits | Published range (source) |
|---|---|---|
| Professional shock chlorination | First step after a positive bacteria test | $80 to $200 (Angi, 2026) |
| Well inspection | After a repeat positive | $250 to $550 (The Well Guide) |
| New sanitary well cap or casing extension | A loose or broken cap, or a casing cut off below ground | Quoted after a look at the wellhead |
| UV system, installed | Bacteria that come back after a shock | $200 to $800 for the unit, plus $150 to $300 to install (The Well Guide) |
| County lab retest | Two to four weeks after treatment | $41 per coliform sample, plus $50 per appointment (Frederick County Health Department) |
| Replacement well | Contamination that persists after repeated disinfection | $8,000 to $20,000 (The Well Guide) |
Why does coliform come back after a well is shocked?
Shock chlorination only kills the bacteria already in the system. Frederick County’s health department says it will not provide a permanent solution to an ongoing contamination problem. Bacteria found after chlorination are evidence that contamination continues to enter the system. The path in is still open.
The county points to four places to look: the groundwater, the well, storage and the plumbing. The University of Maryland Extension handout adds that total coliform may regrow in the water system. It says repeat disinfection is not unusual when bacteria have been growing in the system for a while. If repeated attempts fail, the handout says well cleaning may be needed on top of disinfection.
A repeat positive calls for finding the opening, and a well inspection checks the wellhead for it. If the opening cannot be closed, UV light for well water treats the water as it passes the lamp. It needs clear water to work, so a sediment filter goes in ahead of it. For E. coli, The Well Guide pairs UV with structural well repair, since contamination otherwise recurs.
When should you retest well water after treatment?
Retest once the chlorine is gone, then again two to four weeks after treatment. Frederick County says a sample with chlorine left in it will not give a valid bacteria result. The handout from University of Maryland Extension sets the later retest because total coliform may regrow in the water system.
A home sale adds its own steps after a bacteria failure on the well. In Frederick County, a certificate of potability needs two bacteria samples collected at least 24 hours apart. The county health department generally takes longer to return results than private labs. Book certified lab water testing once the chlorine is gone, and build the lab’s wait into the closing date.
What Maryland rules apply when a well tests positive?
Under COMAR 26.04.04.24, whoever works on a well after the driller’s disinfection is responsible for disinfecting it. If bacteria persist after repeated disinfection, the approving authority may require the well to be abandoned and sealed. After a flood, MDE says not to drink or wash with the water until the well is disinfected.
The disinfection rule covers any contractor who opens the well, our crew included. It applies to a pump swap or any other work done on the well after the driller’s disinfection. HydroWells is licensed through the Maryland State Board of Well Drillers. If you want to read the procedure, Frederick County’s health department posts MDE’s well disinfection steps in printable form.
Got a positive coliform result, or a well that keeps failing its bacteria test? Call (301) 393-7090. We are open 24/7 and take calls nights, weekends and holidays. Estimates are free and written after a look at the property. You can also send us the address and your lab results.