Water Sources, Hydrology, and Source Water Protection
Start with the vocabulary of supply. Surface water (rivers, lakes, reservoirs) is open to runoff and weather; groundwater (aquifers, wells, springs) is filtered through soil and generally more stable in temperature and turbidity but can carry dissolved minerals, iron, manganese, and, in some settings, pathogens or nitrate. A watershed is all the land draining to a source; protection means controlling what enters it. Know safe yield (the dependable withdrawal a source can sustain), drought and seasonal variability, intake siting, wellhead protection areas, and setback distances from contamination. Understand the hydrologic cycle terms (precipitation, infiltration, percolation, runoff, recharge, evapotranspiration) and how each affects raw-water quality.
Traps: questions that blur withdrawal rate with recharge rate, or that call a spring "groundwater under the direct influence of surface water" (GWUDI) without evidence of surface connection. Another trap is confusing source water protection (voluntary/stakeholder, land-use) with treatment. Remember total maximum daily load (TMDL) and source water assessment concepts only at a high level.
Rule of thumb: if a source's quality swings quickly with rain, treat it as surface-influenced. Worked example: a well pumping 500 gpm with a measured recharge of 400 gpm is being mined; the sustainable withdrawal is below 400 gpm, so plan for storage and demand management rather than more pumping.