MN Water Operator common mistakes
MN Water Operator · Understand the traps and how to avoid them.
Computing disinfection CT credit from theoretical detention time (tank volume ÷ flow) without applying a baffling or short-circuiting factor, then reporting the result as contact time achieved.
Volume-over-flow is the only detention formula taught in basic math review, and tank geometry, inlet/outlet arrangement, and density effects are invisible in that calculation, so the shortcut looks complete.
What to do instead
Before any CT calculation, assign a documented baffling factor (from a tracer study or a conservative default for the tank type) and show it as a separate line in the calculation; write the assumed factor on the disinfection log so a reviewer can see the assumption.
Backwashing filters on a fixed clock schedule (for example, every shift) instead of on terminal headloss or filter-effluent turbidity trigger.
Shift routines and handoff habits harden into schedules, and a filter that 'looks fine' gives no immediate feedback that it is loaded.
What to do instead
Post the approved backwash triggers at the filter console and require the operator to record both the trigger value (headloss or effluent turbidity) and the time on every backwash entry; investigate any backwash that fires without a documented trigger.
Recording static pressure at a hydrant and reporting it as the system pressure at that location, skipping residual pressure under flow.
Static pressure is quick, safe, and requires one gauge, while a flow test needs a second hydrant, a diffuser, and coordination; under time pressure the easy number gets written down.
What to do instead
Whenever pressure adequacy is being judged, perform a two-hydrant flow test, record static, residual, and pitot/flow readings plus the hydrant and gauge used, and report residual as the pressure of record.
Approving a high-hazard cross-connection with only an atmospheric vacuum breaker or a hose-bibb breaker (for example, on chemical-injection make-down water or fertigation lines).
The device is familiar, inexpensive, and 'backflow protection' sounds satisfied, while hazard classification (toxicity, pressure, backpressure vs. backsiphonage) is a separate step that is easy to skip.
What to do instead
Classify the hazard first, then select the device from the approved list for that hazard class (air gap or testable reduced-pressure device where required) and put the device on a testable inventory with an annual testing date.
Substituting gauge pressure in psi directly for head in pump, pressure, or horsepower formulas, or mixing gpm and psi without converting.
Gauges read psi and the pump curve may be drawn in feet, and unit conversion is the step most often dropped when a number 'comes out about right.'
What to do instead
Convert every pressure to feet of water (psi × 2.31) before entering a head or horsepower formula, and write the units on each line of the calculation so an unchecked conversion is visible.
Sizing or diagnosing a pump from shutoff head or the nameplate rating instead of the intersection of the pump curve with the actual system curve.
Shutoff head is a single, memorable number on the curve and nameplate data is printed on the pump, while the system curve must be derived from actual static lift, friction, and demand.
What to do instead
Plot the system curve for the real installation, find the operating point where it crosses the pump curve, and verify that point against NPSH available and the motor's service factor before recommending an impeller or speed change.
Reporting a DPD total chlorine result as free chlorine residual on daily logs and reports.
Field kits often run one test, total and free differ by only a few tenths, and the log form frequently has a single 'chlorine' column that invites the substitution.
What to do instead
Use the procedure that separates free from combined chlorine, record both free and total on the log, and calculate combined as the difference so a rising combined residual is visible rather than hidden.
Collecting a total coliform sample from a faucet with the aerator and swivel still attached after a brief flush, or filling the bottle to the very top.
Sampling is treated as a quick errand at the end of a shift, and the sites chosen are the ones nearest the door rather than the ones that represent the distribution system.
What to do instead
Use the approved sample site list, remove the aerator, flush until the water temperature stabilizes, sample without touching the inside of the cap or bottle, leave the required headspace, and record the site, time, chlorine, and temperature on the chain of custody.
Entering a wet well, vault, or other confined space without atmospheric testing, an attendant, or a rescue plan because 'it smelled fine' or the job would only take a minute.
Short jobs feel low-risk, odors do not detect oxygen deficiency or hydrogen sulfide at dangerous levels, and the permit process is perceived as slowing the crew down.
What to do instead
Treat every wet well and vault as a permit-required space: test with a calibrated multi-gas meter before and during entry, ventilate, post an attendant, keep retrieval equipment rigged, and have rescue arranged before the first person enters.
Holding a suspected exceedance or positive result off the record and delaying notification while waiting for a resample or a lab re-check.
Operators want to avoid alarming the public or their supervisor over what may be a sampling error, and the resample feels like the responsible next step.
What to do instead
Notify and report on the schedule the rule sets, not on the schedule confirmation allows: call the primacy agency contact at the first confirmed result, start the correct public notice tier, and document the resample as follow-up in the same record rather than as a substitute for reporting.