9.1 Color, Taste, Odor, and Temperature
Key Takeaways
- Color results are meaningful only when the record identifies the approved method and whether the result represents apparent color or true color after the method-specified turbidity-removal step.
- Taste-and-odor work is a controlled sensory analysis, not permission for an operator to taste an unknown or potentially unsafe sample.
- Temperature should be measured promptly with a verified device because the sample can quickly move toward room temperature and lose its connection to plant conditions.
- An unusual sensory or temperature result is a diagnostic clue; confirm sampling and analytical quality, compare related data, and investigate before changing treatment.
Four observations, four different questions
The 2025 WPI Water Treatment Operator Class I outline expects operators to analyze, record, and interpret color, taste and odor, and temperature. These measurements can reveal source-water changes, treatment performance, or distribution-system conditions, but none identifies a cause by itself. A defensible result preserves the sample location, time, method, units, and surrounding process data.
| Parameter | What the result describes | What it cannot prove alone |
|---|---|---|
| Color | Light-absorbing or visually colored material under a stated method | The identity or health significance of the material |
| Taste and odor | A controlled sensory response, often recorded by character and intensity or method result | The responsible compound or treatment failure |
| Temperature | Thermal condition at a defined place and time | Why the temperature changed |
Color: state which color was measured
Apparent color is the color observed in the sample as received, so suspended and colloidal matter may contribute. True color is measured after turbidity is removed by the procedure specified in the approved method. The distinction matters: a muddy raw-water sample can show substantial apparent color even when dissolved color is much lower. Never label a result true color merely because the sample looked clear.
EPA Method 110.2 is a platinum-cobalt color method intended for color from naturally occurring materials. In that procedure, turbidity can interfere and is removed by centrifugation for a true-color determination. A plant must use its approved method and standard operating procedure (SOP); filtering is not an automatic substitute because a different preparation can change what is removed. Record the method, sample treatment, applicable color units, instrument or comparator, and quality checks.
Natural organic matter may create yellow-brown color. Iron or manganese, algae, corrosion products, treatment chemicals, or disturbed deposits may also change appearance. These are hypotheses, not conclusions. Compare raw, settled, filtered, and distribution samples as appropriate, plus turbidity, metals, pH, weather, chemical-feed, and complaint records. A step change confined to one location suggests a different investigation from a plant-wide raw-water increase.
Taste and odor: controlled sensory evidence
Taste and odor are related but not interchangeable. An odor can be detected without tasting, and temperature can change how volatile compounds are perceived. EPA Method 140.1 is an example of a threshold-odor procedure: a sample is diluted with odor-free water until the least definitely perceptible odor is found under controlled conditions. The operator follows the method for sample temperature, dilution series, panel suitability, and reporting rather than improvising a sniff test.
Never taste an unknown sample or one that may be unsafe. A formal taste procedure may be performed only when the approved method, laboratory safety rules, and sample suitability allow it. Analysts should avoid perfume, smoke, food, illness, or room odors that can bias sensory response. Use neutral descriptors authorized by the SOP, such as earthy, musty, chlorinous, sulfur-like, or metallic, without claiming that a descriptor proves a specific compound.
Temperature: measure before the sample changes
Temperature is commonly measured with a verified thermometer, thermistor, or approved multiparameter device. Measure at the required location or promptly after collection; a bench sample warms or cools toward the room and cannot be chemically preserved back to its original temperature. Record units, location, depth or tap where relevant, time, device ID, and any unusual sampling condition.
Temperature helps interpret other results. It affects reaction rates, gas solubility, viscosity, biological activity, odor release, disinfectant behavior, and treatment response. It may also help explain seasonal coagulation changes or an apparent sensory shift. Those relationships do not create one universal acceptable temperature for every WPI jurisdiction. Compare with the plant's baseline, SOP, authority requirements, and related measurements.
Separate a valid result from a valid diagnosis
Analytical validity and operational meaning are two gates. A color comparator can pass its check while a mislabeled sample makes the result useless for the intended location. When confirmation supports a real change, use the pattern to select the next evidence: a raw-only change points toward source conditions; a change after one treatment step points toward that barrier; one neighborhood's complaints may point downstream.
Records should allow another operator to reconstruct the finding. Include the original result, any dilution or preparation, sensory panel or analyst information required by the method, device checks, comparison samples, process conditions, notifications, and corrective actions. Never overwrite the first result with a cleaner repeat.
Operator decision sequence
- Confirm the sample. Check point, time, labeling, flushing or collection procedure, and preservation limits.
- Confirm the test. Review calibration or verification status, blanks and standards, sample preparation, analyst conditions, units, and method range.
- Compare patterns. Use upstream/downstream samples, historical trends, process changes, weather, and customer-complaint location.
- Escalate appropriately. Repeat or recollect only as the method permits, notify the responsible role, and investigate likely sources.
- Document the decision. Preserve the original result, confirmation work, comparisons, actions, and outcome.
Scenario: a musty report after a storm
A finished-water sample receives a musty odor report while raw-water color and turbidity have also risen. The best first response is not to raise oxidant feed from the complaint alone. Verify the complaint/sample locations and times, check sensory-test controls and current process data, compare raw through finished results, and follow the plant response SOP. The shared timing may support a source-water event, but sampling artifacts, a localized distribution condition, and analytical bias remain possible until the evidence separates them.
Official source trail
A raw-water sample has high turbidity. The operator needs a reportable true-color result under a method that specifies centrifugation. What is the best action?
A bench sample collected an hour ago is now much warmer than the source-water line. Which temperature should be entered as the source-water condition?
A customer describes an earthy odor. What conclusion is justified from that descriptor alone?