LA Water Operator common mistakes
LA Water Operator · Understand the traps and how to avoid them.
On chemical dose problems, the candidate submits a lb/day answer without dividing by the decimal purity of the product (e.g., uses 65 instead of 0.65 for 65% hypochlorite) or drops a unit conversion between MGD, gallons, and pounds.
The lb/day formula gets memorized as a bare string of numbers, and under time pressure the candidate plugs in the label percentage directly and never writes the units through the calculation.
What to do instead
Write the full dimensional equation every time, including a purity term written as a decimal, and cancel units line by line before multiplying. Before moving on, bracket the answer: for a 1 MGD plant, a 1 mg/L dose should land near 8.3 lb/day, so a factor-of-ten result is caught immediately.
On disinfection credit questions, the candidate computes CT as concentration times time only, ignoring the temperature, pH, or baffling-factor correction, or applies the table using the wrong flow (design versus actual peak hourly).
CT is treated as a single arithmetic operation rather than a lookup with correction factors, and the candidate does not identify which flow the rule requires for the calculation.
What to do instead
Work CT in a fixed four-step order: measure residual and contact time, identify the required table value at the measured temperature and pH, multiply contact time by the baffling factor, then compare. Underline the word 'peak hourly' or 'design flow' in the stem and confirm which one the regulation specifies before choosing a number.
On distribution hydraulic questions, the candidate assumes flow splits evenly at a junction or between parallel pipes regardless of diameter, length, and C-factor.
Diagrams with two outlets look symmetrical, and the candidate reasons by geometry rather than by head loss, which is the actual driver of flow split.
What to do instead
Force a continuity check at every node (flow in equals flow out) and rank parallel paths by head loss, remembering that head loss rises sharply with smaller diameter and lower C-factor, so the larger, smoother, shorter pipe carries disproportionately more flow. Practice two or three parallel-pipe problems until the ranking is automatic.
The candidate specifies a pressure vacuum breaker or a simple check valve on a service with a downstream booster pump, chemical injection, or elevated storage that can create backpressure.
The candidate memorizes devices as a list of names rather than as a decision tree, and picks the device with the friendliest sounding name instead of matching the hazard.
What to do instead
Use a two-branch decision rule: first ask whether backpressure is possible (pump, elevated tank, steam, chemical feed) versus backsiphonage only. Backpressure requires an air gap or an RPZ; backsiphonage-only protection can use a PVB, AVB, or air gap. Memorize the protection hierarchy air gap, then RPZ, then PVB, then AVB, then atmospheric vacuum breaker.
On coliform rule questions, the candidate uses the old total coliform sample-count table, or fails to state that repeat samples must be collected within 24 hours of learning of a positive result.
Study material from prior rule versions sticks in memory, and the routine monthly sampling schedule is rehearsed far more often than the exception path that follows a positive.
What to do instead
Rehearse the current rule's population-based routine sample table and treat the positive-result path as its own script: repeat samples within 24 hours (three, or as the primacy agency specifies), plus any required additional routine samples the following month. Draw the flowchart once from memory and check it against the rule text.
The candidate batches samples in a cooler and analyzes chlorine residual or turbidity hours later, or fills the chlorine bottle with headspace and stores it before analysis.
Field collection is treated as a logistics task separate from the analytical method, so preservation and holding time are never linked to the specific parameter in the candidate's mind.
What to do instead
Build a parameter-by-parameter table with four columns: container, preservative, holding time, and field versus lab analysis. Chlorine residual is analyzed immediately on site with no headspace and no storage; turbidity is analyzed promptly. Recite the table before every sampling question so the handling step is part of the answer, not an afterthought.
On confined-space items, the candidate skips the pre-entry atmospheric test or tests in the wrong order, and accepts an entry without a permit, attendant, or retrieval system in place.
The steps get compressed into 'test the air and go in,' and the candidate treats the attendant and permit as paperwork rather than as conditions of entry.
What to do instead
Lock in the sequence: test oxygen first (a combustible meter reading is unreliable in oxygen-deficient air), then flammables, then toxics, then continuous monitoring during occupancy. State the non-negotiables as a chant: permit posted, attendant at the entrance, retrieval or rescue in place, ventilation running. If any one is missing in the stem, the correct answer is no entry.
On a chlorine release question, the candidate selects spraying water on a liquid chlorine leak or approaches the leak from downwind to shut the valve.
Water is the intuitive response to a chemical spill, and the candidate has not internalized that water plus liquid chlorine produces more gas and corrodes the container.
What to do instead
Anchor the exception in memory: water is used only as a fog to knock down vapor, never applied to the liquid or the container, and never into a leaking cylinder. Then apply the approach rule: from upwind, at the highest ground, with the appropriate level of respiratory protection, and evacuate before attempting control. Practice two chlorine scenarios that hinge on the water exception.
On public notification questions, the candidate assigns the 24-hour Tier 1 notice to a monitoring or reporting violation that actually carries the annual Tier 3 notice.
Every violation feels urgent, so the shortest deadline seems safest, and the candidate never learned the tier-to-violation mapping as a table.
What to do instead
Build a three-row table and memorize it by violation type, not by gut feel: acute health risk (e.g., an MCL exceedance with immediate risk) is Tier 1 at 24 hours, other MCL or treatment technique violations are Tier 2 at 30 days, and monitoring, reporting, and recordkeeping violations are Tier 3, typically annual. Match the violation type first, then read the deadline off the table.
The candidate misses the Consumer Confidence Report cycle, either delivering after the July 1 deadline or forgetting that distribution and the certification of delivery are separate required steps after the report is written.
The CCR is studied as a document to be produced rather than as a three-part cycle of prepare, deliver, and certify, so the delivery and certification dates never get anchored.
What to do instead
Put the CCR cycle on a calendar with the state's allowed alternate date: finalize content, deliver to all bill-paying customers by the deadline, and submit the certification of delivery to the primacy agency. When a CCR question appears, check which of the three steps the stem is actually testing before choosing an answer.