Water Quality and Laboratory Analysis
Core concepts
Know the meaning and monitoring of turbidity, disinfectant residual, pH, temperature, and microbial indicators. Understand that coliform bacteria are indicator organisms: their presence signals possible contamination and treatment failure. Grasp sampling fundamentals: representative samples, proper containers, holding times, preservation, and chain of custody. Know the difference between field measurements and laboratory confirmations.
Traps to watch
Questions confuse a positive total coliform result with confirmed fecal contamination; total coliform triggers investigation and repeat sampling, and fecal indicators escalate response. Watch for holding-time violations that invalidate samples. Remember turbidity is measured in nephelometric units and is a treatment-performance indicator, not a pathogen count. Do not confuse chlorine residual (what remains) with demand (what was consumed).
Worked example
Rule of thumb: a sample is only as good as its handling. If a chlorine residual sample is held too long or exposed to light and air, the residual decays and the result understates plant performance. Treat holding time and preservation as part of the measurement, not paperwork.
Study tip
For any monitoring question, ask: what does this parameter indicate, and what action does an out-of-range result trigger?