Drinking Water Distribution - Ohio Operator Study Guide
Drinking Water Distribution tests whether you can keep treated water safe from the plant to the meter. Ohio exam items focus on pressure, disinfectant residual, cross-connection control, storage, main repairs, coliform sampling, and public notification.
Core rules
- Maintain positive pressure: normally not less than 20 psi at all points in the distribution system. Negative pressure or a drop below 20 psi can allow contamination.
- Keep a disinfectant residual throughout the system; for free chlorine systems, do not let representative points fall below 0.2 mg/L. Chloraminated systems must monitor total chlorine and ammonia and control nitrification.
- Control cross connections by containment at the service connection. Approved backflow assemblies include air gaps, RPZs, DCVAs, and PVBs; test them on the required schedule and keep records.
- New mains and repairs follow AWWA C651: chlorinate, flush, and collect bacteriological samples before service. A pressure loss triggers flushing, disinfection, and a boil-water advisory.
- Storage tanks need turnover, mixing, inspection, and residual monitoring to prevent stagnation and DBP growth.
- Total coliform positives require repeat samples within 24 hours; E. coli is an acute MCL with Tier 1 public notice.
Worked example
A 12-inch main break drops area pressure to 5 psi for four hours and affects 200 services. Because pressure fell below 20 psi, assume contamination is possible. Repair the main, flush, disinfect, and issue a boil-water advisory. Collect repeat bacteriological samples; do not lift the advisory until two consecutive rounds are negative at required intervals and residual is restored. The reasoning: the trigger is pressure loss, not visible dirt.
Traps
Checking residual only at the plant; using total chlorine where free chlorine is required; forgetting annual backflow testing; treating 20 psi as a target rather than a minimum; and lifting a boil advisory after one negative sample.