Frequently Asked Questions About Groundwater

How does groundwater move?
Groundwater moves through small openings found in rocks and sediments under the influence of gravity. This natural phenomenon allows surface water and groundwater generally to move from higher elevations to lower elevations.

What is an aquifer?
An aquifer is a saturated geologic layer that is porous and permeable enough to yield useable quantities of water to wells, springs, or surface water bodies. Most aquifers in the state are beds of sand and gravel. However, some wells in areas of Northeast Mississippi use aquifers comprised of fractured rock layers. Aquifers should not be considered as underground rivers or lakes.

How do unconfined and confined aquifers differ?
An unconfined aquifer contains groundwater at atmospheric pressure and is not overlain by adequate confining (clay) layers. The upper limit of the zone of saturation below land surface is commonly referred to as the water table. The depth to the water table usually fluctuates to some extent depending on the season of the year and the amount of local precipitation that directly recharges such aquifers. Because the water table generally conforms to the local surface topography, the depth to water increases in areas of higher relief and decreases in areas of lower elevation.

Groundwater contained in confined aquifers is isolated by relatively impermeable confining layers and is subjected to pressures (or artesian heads) higher than atmospheric pressure. This phenomenon allows groundwater under natural pressure to rise to some level above the actual top of the aquifer. Confined aquifers typically are found in most areas of the state at depths of 200 feet or more.

What is an artesian well?
The geologic layers that comprise aquifers in Mississippi naturally dip at some angle below land surface from outcrop areas where they receive recharge from localized precipitation. Water percolating into these areas moves down dip under the influence of gravity to progressively greater depths as the distance from the outcrop area increases. At depth, clay layers found in abundance in most areas of Mississippi confine these aquifers. The pressure or head exerted by the weight of the water at higher levels in such confined aquifers allows the water to rise above the top of the aquifer in wells that penetrate it down dip from the recharge area. These wells are referred to as artesian wells, even though the water may not flow out naturally at the surface. In some instances, wells located in lowland areas, may penetrate confined aquifers with enough natural pressure that water will flow out on the surface without the aid of a pump. Under such conditions, artesian flowing wells or free-flowing wells are developed.

From where is our drinking water supply derived?
Over 93% of drinking water supply in Mississippi originates from the eighteen major aquifers in the state. Only three public surface water systems presently operate in the state: (1) the city of Jackson uses a combination of ground water and surface water from the Ross Barnett Reservoir/Pearl River; (2) the cities of Tupelo and Fulton receive their drinking water from the Tombigbee River; and (3) Short-Coleman Water Association diverts water from Pickwick Lake.

What is the average depth of a public drinking water well in Mississippi?
The average depth of public water system wells in Mississippi is about 780 feet. Public water system wells range in depths from 56 feet in Newton County to almost 2800 feet in Wayne County. Most public water systems operating in the state obtain their water from deep confined aquifers that are afforded a great deal of natural protection from contamination.

Do I need a permit for my well?
It depends. All wells with surface casing diameters 6 inches or greater generally require groundwater withdrawal permits. However, all wells, regardless of size, that will be used for domestic purposes are excluded from permitting. If you are unsure whether or not a well requires a permit, please contact the agency

How much does a permit cost?
A groundwater withdrawal permit costs $10 and is good for ten years.