Coliform and E. coli in drinking water

Bacteriological sampling is unforgiving. Technique at the tap, the right bottle and the clock all decide whether your sample can be used.

Bottles

The lab supplies sterile 120 mL bottles. Use a sodium thiosulfate-treated bottle for chlorinated water and an untreated bottle for unchlorinated water.

At the tap

1. Use a cold tap.
2. Remove the aerator.
3. Disinfect the outlet.
4. Flush for 2 to 3 minutes.
5. Collect 100 mL.
6. On the COC, note the chlorine residual, source type and exact collection time.

The clock

• Ship immediately after collection.
• Public water system compliance: no more than 30 hours from collection to the start of incubation. Recreational water windows are shorter.
• Hold between 0 and 10°C. Do not freeze.

Which test

Both run on SM 9223B (Colilert-18) under NJ NELAP. A 24-hour turnaround is available if you need results urgently.

If a result is positive

• Public water systems: collect the required repeats within 24 hours of notification and contact your primacy agency. Whether a violation exists depends on those repeats, so do not issue public notification before that unless your agency directs it.
• Private wells: stop using the water for drinking, cooking and brushing teeth, and contact your local health department. Boiling is an interim measure.

Download the coliform and E. coli COC (PDF).