What To Do If Your Water Test Shows Coliform Contamination

A positive coliform result often creates immediate worry, especially for families with children or immunocompromised members. The good news is that a positive result does not always mean your household is in danger, but it does mean something in your water system needs attention. Coliform bacteria act as a warning sign: they indicate that outside material has entered your water supply. Here is what to do next and how to restore confidence in your water.

1. Understand What the Test Result Means

Coliform contamination usually means that environmental bacteria—originating from soil, vegetation, or surface water—have found a way into your plumbing, well, or fixtures. These organisms are not always harmful on their own. Instead, they indicate that conditions exist where harmful bacteria such as E. coli could also enter. When a bacteria screening test reveals coliforms, it is signaling that further action is needed to protect the household.

2. Stop Drinking the Water Until You Identify the Source

While coliforms are not always dangerous, they often appear under the same conditions that allow harmful bacteria to spread. It is best to switch to bottled water or an alternative water source for drinking and cooking until you understand the cause of the contamination.

3. Look for Recent Events That May Explain the Problem

Coliform contamination often follows storms, well disturbances, filter changes, plumbing repairs, or long periods of water stagnation. Even small disruptions can allow contaminants to enter the system. Identifying the possible cause helps determine whether flushing, sanitizing, or more extensive intervention is needed.

4. Flush the Plumbing System Thoroughly

Flushing helps remove loose sediment and clear stagnant zones where bacteria multiply. Each faucet should run long enough for fresh water to travel from the main line or pressure tank to the tap. If the home uses a well, flushing helps bring newly drawn groundwater through the system.

5. Sanitize the System if Necessary

If contamination persists, the plumbing or wellhead may need disinfection. Some homeowners perform a whole-house shock chlorination, while others prefer to have a professional handle the process. Shock treatment helps eliminate biofilm and resets the system for clean operation.

6. Retest to Confirm the Problem Is Resolved

A follow-up bacteria test is essential. Without retesting, there is no way to know whether contamination has cleared. Another bacteria screening kit is ideal for this step because it provides rapid confirmation without waiting for laboratory results. Many homeowners test twice—once immediately after sanitizing and again a few days later to ensure stability.

7. Investigate Long-Term Fixes for Recurring Contamination

If coliform issues return repeatedly, the well cap, casing, plumbing vents, or nearby soil conditions may need evaluation. In older homes, corrosion and biofilm often cause recurrent contamination. In wells, surface water may be entering through damaged seals.

By A. Anagnos, Biomedical Engineer