The Basics of Groundwater

Click on the images for more photos and examples of groundwater discharge.

Most people are surprised to learn that almost all of the world’s unfrozen fresh water exists under the ground. Pennsylvania, having a humid climate, has a lot of water in streams, lakes, and wetlands. But Pennsylvania has much more fresh groundwater than surface water - more than thirty times as much.

Every day, groundwater is taken from wells and springs to meet our household, agricultural, and industrial needs. Unfortunately, we cannot always find enough groundwater for a particular need, and sometimes the groundwater we find cannot be used because of its quality. To avoid these problems as much as possible, we need to understand some basic concepts about groundwater, specifically about groundwater in Pennsylvania.

Read more on the basics of groundwater in The Geology of Pennsylvania's Groundwater, (PDF* 4.36 MB) Pennsylvania Geological Survey Educational Series 3.

Groundwater is an important yet mostly hidden part of the hydrologic cycle. Infiltrating rain and snowmelt supplies our aquifers with water. But what goes in as recharge also comes out. Groundwater discharge as base flow supplies on average over 60 percent of water to streams and rivers, and in times of drought, nearly all flow.  Pennsylvania’s abundant springs are groundwater discharge points. Groundwater wells are manmade discharge points. But whether it is through water wells or natural discharge into stream water, ultimately all Pennsylvanians rely on groundwater. 

Bad Hydrogeology – Misconceptions about groundwater by Gary Fleeger.

Links to other documents that describe the fundamentals of groundwater:

• U.S. Geological Survey Earth's Water: Ground Water
• U.S. Geological Survey Basic ground-water hydrology
• U.S. Geological Survey Ground Water and Surface Water A Single Resource
• Pennsylvania Department of Environmental Protection Groundwater – Pennsylvania’s Cool Resource
• Water Resource Education Network (WREN) Groundwater – A Primer for Pennsylvanians
• U.S. Environmental Protection Agency Ground Water Primer

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