Source Water and Water Quality
What the exam expects
Source water questions test whether you understand where water comes from, what can contaminate it, and how source conditions drive every downstream decision. Know the difference between groundwater (protected from surface contamination, stable temperature and chemistry, often high in dissolved minerals, iron, manganese, hardness, and sometimes arsenic or nitrate) and surface water (rainfall- and snowmelt-fed, turbid, variable in quality, vulnerable to pathogens, algae, and runoff). Springs and infiltration galleries sit in between. Understand watershed protection as the first barrier in the multiple-barrier concept, and know that total organic carbon (TOC) in source water reacts with chlorine to form disinfection byproducts (DBPs).
Concepts to master
- Contaminant classes: microbial (Giardia, Cryptosporidium, viruses, bacteria), inorganic chemicals (nitrate, arsenic, lead, fluoride), synthetic organics (solvents, pesticides), and radionuclides.
- Turbidity as both an aesthetic and a treatment-performance indicator; low-turbidity source water still requires disinfection.
- Algal blooms raising pH and TOC, causing taste-and-odor and filter clogging.
- Seasonal variation: spring runoff spikes turbidity; summer stratification in reservoirs changes intake quality; winter low flows concentrate pollutants.
- Source Water Assessment and wellhead protection areas.
Traps
Questions often swap groundwater and surface water characteristics, or imply that clear water is safe water. Clear water can carry viruses and dissolved nitrate. Another trap: assuming a protected well cannot be contaminated by a nearby septic system or agricultural field.
Rule of thumb
If a stem describes high, variable turbidity and pathogen risk, think surface water needing full conventional treatment; if it describes stable quality, high hardness, and iron, think groundwater, likely needing only disinfection and possibly iron/manganese removal.