Interpreting Bacteria Results

Interpreting results of a total bacteria test:

The detection range of the total bacteria test is 500-10000 CFU/mL. Microbial load is expressed in colony-forming units of bacteria per millilitre of water (CFU/mL) in order to translate the result for comparison to the US Environmental Protection Agency’s (EPA) standards. According to US EPA guidelines, drinking water is required to have less than 500 CFU/mL of total heterotrophic bacteria and no detectable amount of E.coli.

For total microbial load, your results can be interpreted in the following way:

Range Interpretation Treatment Recommendation
< 500 CFU/mL Total microbial load is below the recommended limit and treatment is not required. Maintain on-going testing and your current treatment plan.Revise your treatment plan if needed to maintain this bacteria level between tests.
500 - 2000 CFU/mL Total microbial load is moderately low. The issue may be localized or seasonal. Do not drink water from this source until the microbial load is decreased. The total microbial load is above the recommended limit, but not dangerously. Retest to confirm results and schedule system maintenance as needed.
2000 - 5000 CFU/mL Total microbial load is moderately high. Biofilm may be developing in the water source. Water from this source is not safely drinkable. Immediate treatment is required. Test upstream to determine the source of the issue. Replace parts as needed or increase disinfection and retest over time. 
> 5000 CFU/mL Total microbial load is high. Biofilm has likely developed and water from this source should not be used for drinking, bathing or swimming. Immediate aggressive treatment is required. Test points upstream to determine if the issue is widespread. Replace parts as needed or increase disinfection and retest over time. 

For disinfection plan recommendations, see the following help article:

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