Storms cause increased ...

Storms cause increased run-off and aquifer recharge. Both can have an impact on water quality. On the one hand, if there agricultural areas nearby, the pollutants contained in fertilizers (e.g., phosphate, nitrate and friends) may be flashed and reach surface water bodies. Not to mention (as Felicien partly did referring maybe to human open defecation, also common) is there's ranching industry nearby. That means a party of Scherichia Coli in your water. On the other hand, the pollutants can also reach aquifers and contaminate ground water. Ways to tackle this problem: many. First of all, culture (e.g., no stinky open defecation). Second, more culture and increasingly restrictive laws, on modern, less potentially contaminant fertilizers. Third, more culture on storage of animal stinky sub-products. Fourth, modelling of flood risk and of the corresponding correction measures. Hope this helps.