WA Water/Wastewater Operator common mistakes
WA Water/Wastewater Operator · Understand the traps and how to avoid them.
Computing a chlorine dose, detention time, or flow conversion and turning in the raw arithmetic result without checking that the units match the answer choices (e.g., leaving pounds where mg/L was asked, or mixing gallons and cubic feet).
Candidates memorize formulas like Dose (lb/day) = Flow (MGD) x Concentration (mg/L) x 8.34 but plug numbers in without tracking units, and the exam deliberately offers distractors that are the right number with the wrong unit or a factor-of-8.34 error.
What to do instead
Before calculating, write the target unit at the end of the equation and cancel units through each step; after calculating, compare against the answer set and eliminate any choice whose magnitude is off by roughly 8.34, 1,000, or 0.785 (circle area factor). Practice 10 dose and detention-time problems per study session with units written out.
Answering process-control questions by picking the 'normal operating range' remembered from a textbook instead of interpreting the scenario data given (e.g., choosing a typical chlorine residual when the stem states the residual is low and coliforms are present).
Candidates prepare by memorizing ranges and setpoints, so under time pressure they pattern-match to the familiar number rather than reading what the stem's data imply about the cause.
What to do instead
For every scenario question, underline the given values and the observed problem, then ask 'what does this data point to?' before looking at choices; eliminate any choice that is a normal value rather than a corrective action for the stated condition.
Confusing the direction of a relationship or the consequence of a change - for example, saying that increasing filter loading rate improves turbidity, that higher temperature always increases chlorine residual persistence, or that a longer detention time in a settling basin decreases removal.
Many exam items test cause-and-effect reasoning (loading rate vs. effluent quality, CT vs. inactivation, SVI vs. settling), and candidates who memorized isolated facts without the directional link guess the wrong sign.
What to do instead
Build a one-page 'if this goes up, that goes...' table for each process (filtration, sedimentation, coagulation, disinfection, activated sludge) and rehearse it; when a stem describes a change, state the direction of the effect in words before choosing.
Missing the distinction between similar-sounding regulatory requirements: reporting vs. monitoring deadlines, Tier levels, public notice timeframes, and which contaminants have MCLs vs. treatment techniques.
Regulatory content is dense and the exam uses near-identical phrasing across choices; candidates study the rule's purpose but not its specific clock (e.g., 24 hours vs. 30 days) or its category.
What to do instead
Make flashcards with the specific number and trigger on the front (e.g., 'Tier 1 public notice deadline', 'total coliform MCL') and the exact requirement on the back; drill until the number is recalled without hesitation.
Mixing up collection system and distribution system concepts - applying distribution pipe velocity or pressure criteria to gravity sewers, or confusing infiltration/inflow with unaccounted-for water.
Both domains involve pipe networks and flow, so candidates transfer terminology incorrectly, especially under items that describe flow in a gravity line.
What to do instead
Create a side-by-side comparison chart: driving force (gravity vs. pressure), design slope/velocity, typical problems (roots, grease, sags vs. dead ends, cross-connections), and key terms; review it before each practice set.
Selecting a pump or motor answer based on the equipment name alone rather than reading the operating condition described (e.g., choosing a positive-displacement pump for high-flow low-head service, or ignoring that the stem describes cavitation symptoms).
Candidates learn pump types as definitions but not their application envelopes, so they miss items that require matching the pump curve or symptom to the correct hardware or cause.
What to do instead
For each pump type, note its best-fit service (flow/head, viscosity, metering accuracy) and its characteristic failure symptom; when a stem lists symptoms, name the mechanism (cavitation, air binding, worn impeller) before reading choices.
Treating safety items as generic 'be safe' answers instead of applying the specific hierarchy - for example, choosing PPE over engineering controls for confined space, or missing lockout/tagout or atmospheric testing sequence questions.
Safety content feels intuitive, so candidates skim it and pick the most cautious-sounding option rather than the procedurally correct one.
What to do instead
Review the confined-space entry sequence (permit, isolate, ventilate, test, attendant, retrieval) and the hierarchy of controls as ordered lists; on safety items, choose the answer that reflects the required procedure or the highest-level control, not the most cautious wording.
Reading only the last sentence of a multi-sentence stem and answering the wrong question - e.g., the stem asks what should be checked FIRST or what the MOST LIKELY cause is, and the candidate answers what the corrective action would be.
Stems are long and candidates skim to save time, latching onto a keyword like 'chlorine' or 'alarm' and selecting a plausible but non-responsive option.
What to do instead
Read the final sentence (the actual question) first, then scan the stem for the data it asks about; circle qualifiers like FIRST, MOST LIKELY, EXCEPT, and NOT, and verify the chosen option answers that specific qualifier.
On 'EXCEPT' and 'NOT' items and on 'which is the best answer' items, choosing the first true statement encountered rather than evaluating all options.
Under time pressure, recognition of a true fact triggers an immediate selection, and negative stems invert the usual logic so the true statement is the wrong choice.
What to do instead
When a stem contains EXCEPT or NOT, rephrase it as 'three of these are true, one is false' and mark each option T or F before selecting; for best-answer items, rank all options and confirm the winner is more correct than the runner-up.
Guessing at sampling, testing, or recordkeeping procedure details (preservative, holding time, or who signs/submits a report) instead of recalling the specific requirement, and leaving such items blank or rushing them.
These are low-glamour memorization items that candidates deprioritize, yet they appear frequently and are unambiguous if studied.
What to do instead
Maintain a single reference sheet of holding times, preservatives, and reporting responsibilities for the parameters tested at the plant; quiz yourself weekly and flag any item you cannot answer from memory for targeted review.