Source Water and Water Quality
What you must understand
Source water work begins with knowing where the water comes from and what it carries. Candidates should be able to distinguish groundwater (low turbidity, stable temperature, often high hardness, iron, manganese, and dissolved gases; vulnerable to nitrate and volatile organic contamination) from surface water (variable turbidity, color, pathogens, algae, and seasonal swings). Know the classic water-quality parameters: turbidity, color, pH, alkalinity, hardness, temperature, dissolved oxygen, conductivity/TDS, and the contaminant classes regulated under the Safe Drinking Water Act (microbial, disinfection byproducts, disinfectants, inorganic and organic chemicals, radionuclides).
Understand alkalinity vs. hardness-a frequent trap. Alkalinity is acid-neutralizing capacity (bicarbonate, carbonate, hydroxide); hardness is mostly calcium and magnesium. Water can be hard and low in alkalinity, or soft and high in alkalinity.
Know watershed protection and source water assessment: identifying potential contaminant sources, sanitary surveys, and why source protection is cheaper than treatment. Recognize that temperature drives reaction rates, disinfection efficiency, and density currents in reservoirs.
Traps
Questions often swap turbidity (an optical measure of suspended particles) with total suspended solids (a gravimetric measure). Another trap: assuming low turbidity means safe-pathogens like Cryptosporidium survive in clear water. Also watch unit confusion (NTU vs. mg/L) and confusion between primary (health-based, enforceable) and secondary (aesthetic, non-enforceable) standards.
Rule of thumb
Surface water turbidity can change by an order of magnitude within hours after a storm; design and dose for the worst credible raw quality, not the average. A worked check: if raw turbidity rises from 5 to 50 NTU, expect coagulant demand to rise roughly in proportion to particle surface area-verify by jar test rather than guessing.