Positive Coliform Sample at a Public Water System: What Happens Next
The first 24 hours: collect your repeat samples
When the lab tells you a routine sample is total coliform positive (TC+), you have 24 hours from that notification to collect repeat samples.
Collect at least 3 repeat samples for each TC+ routine sample, all on the same day.
Sample from the right taps, as listed in your sample siting plan:
the tap where the positive sample was taken
a tap within 5 service connections upstream
a tap within 5 service connections downstream
Ground water systems: also sample each active source. The Ground Water Rule requires a triggered source sample from every well that was in use when the positive sample was taken.
Record the chlorine residual at each repeat site if your system disinfects.
Get the samples to the lab promptly. Bacteria samples must be analyzed within 30 hours of collection, so plan around weekends and holidays.
Can't make the 24-hour deadline because of logistics, or have only one tap? Call your state field office right away to ask about an extension. In Idaho, DEQ cannot waive repeat samples, only extend the timing. After an E. coli-positive routine sample, no extension is allowed.
If any repeat sample is also TC+, collect another full set of repeats, and keep going until one complete set is clean or a Level 1 or Level 2 trigger is reached.
Systems that normally sample quarterly or annually should also expect extra routine samples the following month. Confirm the number with your field office.
What your repeat results mean
Every TC+ sample is also tested for E. coli. The combination of your routine and repeat results decides what happens next.
Routine sample | Repeat samples | What it means |
TC+, E. coli absent | All TC absent | Repeats are done. Watch your monthly totals: a second TC+ in the same month can trigger a Level 1 assessment. |
TC+, E. coli absent | Any TC+, E. coli absent | Treatment technique trigger. For systems taking fewer than 40 samples a month, two TC+ samples in one month trigger a Level 1 assessment (Level 2 if it's the second trigger in 12 months). |
TC+, E. coli absent | Any E. coli+ | E. coli MCL violation. Tier 1 public notice and a Level 2 assessment. |
E. coli+ | Any TC+ | E. coli MCL violation. Tier 1 public notice and a Level 2 assessment. |
E. coli+ | Not all repeats collected | E. coli MCL violation, even if no more bacteria are found. |
Any | A TC+ repeat not tested for E. coli | E. coli MCL violation, because nobody can show the water is safe. |
An E. coli-positive routine sample with clean repeats is not an MCL violation, but still call your field office the same day.
Assessments: find and fix the cause
The RTCR no longer issues a violation just for finding total coliform. Instead, certain results "trigger" an assessment: a structured look at your system to find the sanitary defect that let bacteria in, and fix it.
Level 1 assessment | Level 2 assessment | |
Triggered by | Two or more TC+ samples in a month (systems taking fewer than 40 samples a month), more than 5% TC+ (40 or more a month), or failing to collect all repeats after a TC+ routine sample | An E. coli MCL violation, or a second Level 1 trigger within a rolling 12 months |
Who does it | The water system | A state-qualified assessor. In Idaho, DEQ or the health district performs it. |
Deadline | Report to the state within 30 days | Report to the state within 30 days |
Common causes assessors find include missing or loose well caps and vents, cross-connections, storage tank hatches and vents, pressure loss during main breaks or repairs, and poorly chosen sample taps.
Public notice
An E. coli MCL violation requires Tier 1 public notice within 24 hours. That usually means a boil water advisory delivered directly to your customers. Failing to complete a required assessment or corrective action is a treatment technique violation, which needs Tier 2 notice within 30 days.
Who to call
Idaho: your DEQ regional office. Call within 24 hours of any E. coli-positive result, or when you need a repeat-sampling extension.
Washington: the Department of Health Office of Drinking Water regional office. In Washington, the lab also notifies DOH of coliform-positive results by close of business the same day.
You'll find contact details on our DEQ Contacts page.
Be ready before it happens
Keep your sample siting plan current, with repeat taps already chosen upstream and downstream of every routine site.
Keep a set of repeat bottles on hand, so you can sample the same day you get the call.
Don't sample on a Friday afternoon unless you know the lab can receive repeats over the weekend.
Use good sampling technique. Many positives come from the tap, not the system: remove aerators, avoid swivel and leaking faucets, flame or disinfect the tap if needed, and never touch the inside of the bottle or cap. See How to Take a Bacteria Sample.
Need repeat bottles fast? Call us
Accurate Testing Labs is a certified drinking water laboratory in Coeur d'Alene, serving public water systems across North Idaho and Eastern Washington. When a positive result comes in, call us and we'll help you get your repeat samples collected and back to the lab within the deadlines.
7950 Meadowlark Way, Coeur d'Alene, ID 83815 Phone: 208-762-8378 Monday–Friday, 7:00 am–3:00 pm. Weekends by appointment; please call during business hours.
This article summarizes the federal Revised Total Coliform Rule as adopted in Idaho (IDAPA 58.01.08) and Washington (WAC 246-290). Your state drinking water program has the final word on requirements for your system.
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