Groundwater, under most conditions, is safer and more reliable for use than surface water. Part of the reason for this is that surface water is more readily exposed to pollutants from factories, for example, than groundwater is. This by no means says that groundwater is invulnerable to contamination. Although it is not as vulnerable as surface water, contaminates can still reach wells and therefore households. Any chemicals that are easily soluble and penetrate the soil are prime candidates for groundwater pollutants. A potential pollution problem can still reach a well miles away through underground water currents. For example, a chemical that spills at an industrial plant miles away, could infiltrate the ground and eventually enter the aquifer system that an entire community uses for their private wells. This situation could have devastating effects: once groundwater is contaminated, it is an extremely costly operation to remove the contaminate.
If we compare an organic pollutant in groundwater to one in surface water water, groundwater has fewer microbes to digest organic pollutants, less oxygen no sunlight and surface from which organic pollutant can evaporate. Especially in slow moving groundwater, pollutants can persist indefinitely.