Water Quality, Sampling, and Disinfection
Water quality and monitoring
The Safe Drinking Water Act sets primary MCLs (health) and secondary MCLs (aesthetic). Florida DEP implements monitoring under Chapter 62-550, F.A.C. Know the big ones: total coliform rule and E. coli, nitrate (10 mg/L as N), arsenic, lead and copper (action levels, first-draw samples), disinfection byproducts (TTHM/HAA5), and turbidity for filtered surface water (≤0.3 NTU in 95% of samples, never >1 NTU). Sampling plans define sites, frequency, and methods.
Disinfection
Free chlorine, chloramines, ozone, and UV each have strengths and CT requirements. Measure residual by DPD; free and total chlorine differ when chloramines are used. Sample handling matters: chlorine residual is measured in the field, bacteriological samples are chilled, preserved as required, and shipped within holding time with chain of custody.
Traps
- Sampling at a non-representative site or after flushing when the plan says first-draw.
- Confusing MCL with secondary maximum contaminant level.
- Reporting a residual taken hours after collection.
- Forgetting that chloramine residuals need different test methods.
Worked example
If required CT for a given pH/temperature/log inactivation is 30 mg·min/L and the measured residual at peak flow is 1.2 mg/L, required contact time = 30 ÷ 1.2 = 25 minutes.
Rule of thumb
Residual × time = CT. Never let the math hide the field reality: measure residual where it matters and at the right flow.