Limestone aquifers provide water to areas throughout the eastern United States, as well as some parts of the southwest. Acidic water carves interconnected openings through underground deposits of this carbonate rock, forming the water storage areas called aquifers. The openings in the rock range from microscopic pores to large channels and caverns. The composition of limestone and the structure of the aquifers can lead to some disadvantages.
Some limestone aquifers consistently yield high volumes of water, but others produce lower volumes or sometimes go dry. Porosity identifies how much water an aquifer can hold, and some less-weathered limestone aquifers have such low porosity that they simply do not contain enough water to be used as a water source.
Many limestone aquifers have high permeability, which measures how quickly water can travel through the ground. Water that moves easily through the aquifer is also more easily pumped out. However, water that is quickly pumped out can also quickly be depleted if the porosity is low.
Large cavities in limestone aquifers contribute to the formation of sinkholes. They can also occur where the limestone rock is exposed on the surface. Over-pumping from an aquifer increases the likelihood of sinkhole formation, as a decrease in underground water pressure can lead to structural failure.
Certain features of limestone aquifers make the groundwater contained in them more susceptible to contaminants. Surface water can enter a sinkhole rapidly, so any contaminants in the surface water will be introduced into the aquifer. Groundwater in limestone aquifers also absorbs calcium and magnesium from the surrounding rock. These minerals create hard water, which can leave deposits in bathtubs and sinks.