If the terms water table and water level mean more or less the same then why do we have two different terms?
Sometimes they mean the same, but not always. While the uppermost level (top) of the saturated zone in an unconfined aquifer is the water table, the water level seen in a well is commonly referred to as water level. When a well is dug in an unconfined aquifer, water from the formation seeps into the well and gradually builds up a water column. The top surface of this water column finally stops rising any further and remains static when it reaches the water table level. The depth of static water level, as seen in a well is also the depth of the water table in the aquifer. Any water level seen in a well that is not static is called the dynamic water level or simply the water level. The depth of dynamic water level always lies below the water table.
When a well is pumped, the water level in the well starts falling. Initially, the rate of water level decline is faster, which gradually slows down as the aquifer starts releasing water into the well simultaneously. The water level will continue to fall as long as the pumping rate remains higher than the release rate of water from the aquifer into the well. However, in a pumping well, if at any point, the quantity of water being pumped out becomes equal to the quantity of water being released by the aquifer, the water level in the well stabilizes and attains a steady-state condition. When pumping is stopped, the water level starts rising again, to begin with at a faster rate which slows down as the dynamic water level approaches the static water level.
Geohydrological studies, amongst others, require collecting water level data from numerous wells throughout the year to obtain the extent of fluctuation in the groundwater table. The water level measured for collecting water level data must essentially be the static water level and not any other dynamic water level. For this reason, any functional well pumped regularly cannot be used for water level monitoring and data collection. Separate observation wells are to be drilled or selected exclusively to collect water level data.
