16.3 Physical Source-Water Characteristics

Physical characteristics describe what the source is doing

A physical source-water characteristic is an observable or measurable property that helps describe the water before treatment. For WPI Class I work, key examples include temperature, turbidity, suspended sediment, color and clarity, source level and flow condition, and taste-and-odor events. These properties matter because they can change quickly with storms, erosion, wildfire effects, reservoir turnover, intake depth, construction, or a source switch. They can also change the treatment demand without identifying a specific contaminant.

Physical, chemical, and biological categories overlap. Algae can contribute turbidity and odor; dissolved organic matter can contribute color; temperature can change biological activity and chemical reactions. The operator uses the categories to organize evidence, then connects all three to source risk and treatment performance. A brown source can contain mineral sediment, organic particles, biological material, or a mixture. Appearance begins the investigation; it does not finish it.

WPI lists formal color, taste/odor, turbidity, temperature, and total suspended solids analyses in the Laboratory domain. This Source Water section addresses what the pattern means at the intake and how the operator responds. The laboratory sections teach methods and result quality.

Interpret turbidity as a signal, not an identity test

Turbidity describes light scattering and absorption caused by material in water. Surface-water turbidity often reflects suspended sediment or algae, but particle size, shape, color, density, and instrument design affect the reading. Bubbles, a dirty cell, fouling, scratches, poor sample handling, or an unrepresentative sample can create misleading values. Verify an abrupt change using the approved check, a grab sample or independent instrument where appropriate, and related source observations.

A storm-driven turbidity rise can increase particle loading, coagulant demand, settled-solids production, filter loading, and the importance of barrier monitoring. It does not prove that pathogens are attached to the particles. Review rainfall, stream flow, upstream activity, intake depth, raw-water color, jar testing, settled-water quality, and individual-filter trends. Use approved process-control steps rather than multiplying a chemical dose from turbidity alone.

Imagine two intakes on the same reservoir. The shallow intake becomes turbid during high wind while the deeper intake remains near baseline. Confirm both sample locations and instruments, review wind direction, intake status, reservoir level, and treatment response, then follow the source-selection SOP if switching is authorized. Do not claim the entire reservoir has one uniform value from a shoreline observation.

Temperature and depth can reorganize the source

Temperature affects water density, viscosity, biological activity, and reaction rates. In deeper lakes and reservoirs, temperature differences can create layers that mix slowly. Seasonal cooling, wind, inflow, or operational changes can weaken layering and alter the quality presented at an intake. A turnover or depth change may accompany shifts in turbidity, color, dissolved oxygen, iron, manganese, odor, or biological activity; it does not guarantee that all will change in every reservoir.

Record temperature with depth and location where the monitoring plan calls for it. Compare intake-water temperature with recent profiles and source elevation. At the plant, colder water may change coagulation, floc formation, settling, filtration, and disinfection behavior. The operator confirms performance through jar tests and process data rather than assuming a fixed seasonal dose. A warm surface bloom also may not describe water drawn from a deeper intake, and a deep sample does not rule out a surface event that could move with wind.

Evaluate color, solids, flow, and sensory evidence together

Apparent color can include suspended material; true color is assessed after the method removes turbidity interference. This distinction helps determine whether clarification may remove much of the visible color or whether dissolved material remains, but it does not identify the compound. Suspended and settleable material indicate physical loading; the actual treatment response depends on particle character and coagulant conditions.

Taste and odor reports are useful surveillance even when the water is not tasted at the plant. Record the reporter location and time, description, persistence, source condition, and whether other customers or source points show the same pattern. An earthy odor can suggest biological activity; a solvent or fuel odor can signal an incident. Neither should be identified by deliberate close smelling. Follow the safety and source-response plan, protect the intake when required, and obtain approved analysis.

Physical-change response sequence

1. Confirm source, depth, time, units, method, and instrument condition.
2. Compare baseline, weather, flow, reservoir level, intake lineup, and upstream observations.
3. Check related chemical and biological evidence without assuming causation.
4. Review jar tests and treatment-barrier performance before an authorized adjustment.
5. Record the verified condition, uncertainty, notification, action, and follow-up.

This sequence turns a visible or instrument signal into a defensible operator decision. It also preserves the most important boundary: a physical change can reveal risk and treatment challenge, but confirmation of a specific chemical or organism comes from the appropriate analysis.

Official source trail

• WPI 2025 Water Treatment Operator Class I Need-to-Know
• USGS primer on water-quality characteristics
• USGS turbidity science
• USGS water temperature science