What is Groundwater?

Water is an important resource for all Albertans. Much of our water comes from surface sources, like rivers and lakes, which are easily accessible. Some of our water, however, is accessed from underground sources to support our growing rural population. This water is commonly referred to as groundwater and resides within the soil and rock formation beneath our feet. This water occurs in two principal zones (Figure 1): 

• the unsaturated zone (or vadose zone); and 

• the saturated zone (or phreatic zone). 

In the unsaturated zone, voids or spaces between particles of clay and silt, sand grains and gravel as well as cracks or fractures within otherwise competent bedrock formations contain both air and water. Although a considerable amount of water can be present in the unsaturated zone, this water cannot be pumped by wells because it is held too tightly by capillary forces. The upper part of the unsaturated zone is the soil-water zone. Within the soil zone, infiltration of water from the surface is enhanced by the presences of roots, voids left by decayed roots, desiccation cracks and animal and worm burrows. Soil water is used by plants during their growth, and is either transpired or evaporated directly from the surface to the atmosphere. 

Figure 1: Distribution of water in the subsurface

In contrast to the unsaturated zone, the voids in the saturated zones are completely filled with water and other fluids like oil and gas. Water in the saturated zone is referred to as groundwater, and the upper surface of the saturated zone represents the water table. Below the water table, the water pressure is great enough to allow water to enter wells, thus permitting groundwater to be withdrawn for use. The depth of the water table is highly variable and can range from zero, when it is at land surface, to great depths beneath some landscapes. Usually, the depth to the water table is small near permanent water bodies of surface water such as streams, lakes and wetlands. An important characteristic of the water table is that its elevation varies seasonally and from year to year. Groundwater recharge and timing of precipitation inherently affect variation of the water table elevation.  

Section 1: Introduction

Module 1: What is groundwater?

Module 2: What is an aquifer?

Module 3: How does groundwater move?

Module 4: What is the role of groundwater in the hydrological cycle?

Module 5: How does groundwater interact with the surface environment?

[1] ESRD. (2014). State of the Environment. Retrieved from http://esrd.alberta.ca/focus/state-of-the-environment/water/default.aspx