Many field-grown crops are irrigated with wastewater that's been partially treated or is recycled from previous irrigation cycles. These are generally considered safe for agriculture, but is not considered safe for human consumption. Some contaminants that may slip by testing include harmful microorganisms that cause illness or even parasites that can take up residence in the human body. Potable (drinking) grade water must meet much higher standards, including zero incidence of e-coli bacteria, and must be transported and stored in a manner that prevents exposure to harmful chemicals.
Since both the water and nutrient solution in a hydropinic setup is all selected by you, you can carefully control what goes into the food you'll be consuming. Problems that you hear about with leafy greens (listeria, e-coli, etc.) that trigger massive recalls are esentially non-existent with hydroponic crops, so long as you maintain careful sanitary standards both while growing and preparing your product.
