Last month, Rajasthan’s Jaisalmer district witnessed a unique geological event. Large amounts of water began pouring out from underground. Rajasthan State Ground Water Department attributed the incident in Jaisalmer to an “artesian condition.”

Artesian Condition

The groundwater in some aquifers can be under pressure. Between layers of poorly permeable rock, such as clay or shale, and may confined under pressure. Sometimes, water will spill out from the well due to artesian pressure. Water confined in this way said to be under artesian pressure, and the aquifer called artesian aquifer.

The word artesian refers to situations where the water confined under pressure below layers of relatively impermeable rock.

Artesian water is not different from other groundwater, except for the fact that it flows to the land surface because pressure in the rocks underground forces it to the surface

Artesian wells require specific geological conditions. First, there must be a permeable layer of rock, such as sandstone or limestone, that can hold and transmit water. This known as an aquifer. Second, this aquifer must be sandwiched between two impermeable layers of rock or clay, which prevent the water from escaping. Third, the water in the aquifer must be under pressure. This usually occurs when the aquifer inclined, so that one end of it is at a higher elevation than the other. When a well drilled into this pressurized aquifer, the pressure can force the water up the well without the need for pumping.

Imagine an artesian well like a sandwich with a juicy filling. The permeable layer of rock, or aquifer, is like the juicy filling that holds water, similar to how a sandwich filling holds flavor. The impermeable layers of rock or clay are like the slices of bread that keep the filling from spilling out. When the aquifer is under pressure, it’s like squeezing the sandwich so that the filling is ready to burst out. Drilling a well is like poking a hole in the sandwich, allowing the juicy filling to flow out without needing extra force.

The four necessary conditions for an artesian well to occur are:

• The basin should be saucer shaped.
• Permeable rock must be present between two non porous rocks.
• The layer of permeable rock should exposed to the ground surface so that water can sink below the surface.
• Rainfall should be enough and sufficient to provide an adequate supply of underground water.

An artesian aquifer a layer of pressurized water captured between layers of underground rock.