Why shouldn’t fruits, vegetables, hands be washed with water taken from open reservoirs before eating?

We all know from childhood that you need to wash your hands before eating, and you need to wash vegetables and fruits before eating. But not all water will help you get rid of germs, bacteria, and parasites.
Water from open reservoirs is full of various effluents and contains a huge amount of bacteria, microbes and other microorganisms. To use it for drinking or cooking, you must first clean it. At a minimum, for disinfection, it is necessary to boil this water, otherwise, if microorganisms contained in the water enter the body, this can negatively affect human health.