PWSs must follow a RIDOH-approved, current coliform sampling plan to meet sampling requirements and to make sure drinking water is tested appropriately. The purpose of the PWS’s coliform sampling plan is to show where and how many water samples must be taken for total coliform monitoring. The sampling plan includes a coliform sampling schedule, requiring total coliform sampling on a monthly or quarterly basis. The circumstances outlined below can cause a change to a PWS’s total coliform sampling frequency. For the latest sampling schedules and results, visit Drinking Water Watch. Instructions for using Drinking Water Watch are available here.
The sampling plan is helpful when a water sample result shows total coliforms are present because it will show where additional required samples need to be collected. Repeat sampling helps to confirm if there is a pathway for microbial contamination within the water system. For more information about properly labeling and submitting the samples to your lab to ensure that results are reported accurately, refer to the Drinking Water Sample Reporting Codes guidance.
If your coliform sampling plan needs to be updated, contact the Rhode Island Department of Health (RIDOH) Center for Drinking Water Quality (DWQ) at 401-222-6867 or email DOH.RIDWQ@health.ri.gov with a subject line containing, “Coliform sampling plan,” name of PWS, and PWS ID number.
What to Do When a Sample Shows Total Coliforms Are Present
A combination of routine and repeat water samples will confirm the presence or absence of total coliforms or E. coli bacteria in the PWS’s distribution system. Download and print the PWS Routine Monitoring for Coliform Bacteria guidance document. This document includes a flowchart that illustrates the sampling process and what actions to take when sample results show that total coliforms or E. coli are present. It is designed to help you put your coliform sampling plan into action. Note: If your PWS takes 40 samples or more per month, parts of the process are different. Contact RIDOH with any questions.
Do not disinfect the water system or increase existing disinfection before collecting repeat, routine, or triggered well samples unless directed to do so by RIDOH.
Well Sampling for Total Coliforms
Total Coliforms Are Present in Well (but E. coli Is Absent), Follow-Up Sampling, and Disinfection
Use this section as guidance when a well sample result shows that total coliforms are present and the result is not from a triggered well sample that was taken because total coliforms were present in the distribution system. A PWS must issue a boil water advisory if they receive E.coli-present sample results from a well that does not have RIDOH-approved 4-log disinfection treatment. To read more about required boil water orders, go to the Emergency Information for Public Water Systems webpage.
If sample results from a PWS’s well show total coliforms are present and sample results from the primary sampling location listed on the coliform sampling plan show total coliforms are absent, the PWS must take a follow-up sample from the primary sampling location within 24 hours. This is a follow-up routine sample, not a repeat sample.
Total Coliforms Are Absent in Follow-Up Routine Sample Results
If the follow-up routine sample results show total coliforms are absent, the well must be disinfected, pumped to waste, and another well sample must be collected to ensure successful disinfection. If the PWS has more than one well, the affected well must be shut off if possible before the PWS proceeds with disinfection, pumping to waste, and sampling the well. Once sample results showing that total coliforms are absent are received by RIDOH and are satisfactory, the PWS will receive approval to place the well back into service.
Total Coliforms Are Present in Follow-Up Routine Sample Results
If the follow-up routine sample results show totals coliform are present, the PWS must conduct repeat sampling and triggered well sampling as required. Use the Well Disinfection Procedure and save it for reference during compliance inspections.