All water supplies are drawn from either ground water, or surface water. Surface water lies on top of the ground, in a pond, lake, river or collection tank. Ground water has soaked into the ground, where it comes to rest in sand or gravel aquifers, or collects in large rock formations, creating underground rivers and lakes. The percolating action as water moves through the soil can remove a number of contaminants. Ground water is usually free of organisms like Giardia (jar DEE uh) and Cryptosporidium. It also tends to be 'harder' than surface water, because it picks up minerals from the rocks on its way down. Surface water is more vulnerable to contamination; in the past, industrial waste was the biggest concern. Now, the greatest threat comes from sources like animal and human waste, pesticides, fertilizers, vehicles, and erosion. Because surface water is easier to access, it's a much cheaper water source. On the other hand, ground water doesn't usually require as much filtration, which may partially offset the cost of pumping it up. To find out more about ground water and surface water, visit your library or bookstore.
