**2. Aquifers**

Aquifers are bodies of rock and/or sediment that contain groundwater. The term "groundwater" refers to rainwater that penetrated through the soil and accumulated in voids of the subsurface of the soil. Aquifers naturally filter groundwater by forcing it to travel through tiny pores and between sediments, which aids in the removal of contaminants. However, this natural filtration process may not be sufficient to remove all of the pollutants. Aquifers are classified into two types: confined and unconfined.

Confined aquifers are also known as "Artesian aquifers" since they are located mainly above the base of confined rock strata. Water levels in punctured wells derived from artesian aquifers fluctuate owing to pressure changes rather than the quantity of stored water. The ruptured wells function primarily as conduits for water transfer from replenishment regions to natural or artificial end destinations.

Unconfined aquifers, in contrast to restricted aquifers, are typically found near the ground surface above the water table, although sitting comparatively above impervious clay rock strata. The water table is the highest barrier of groundwater inside an unconfined aquifer. Groundwater in an unconfined aquifer is more sensitive to contamination by surface pollution than groundwater in confined aquifers due to simple groundwater penetration by terrestrial contaminants. The level of groundwater fluctuates and is determined by the amount of groundwater stored in the aquifer, which impacts the rise or fall of water levels in wells that draw their water from aquifers (**Figure 1**).

### **2.1 Artificial recharge**

Artificial recharge is a strategy for replenishing an unconfined aquifer by sending additional surface water into the earth by distributing it on the surface, using recharge wells, or modifying natural conditions to enhance penetration. Artificial recharge is also known as planned recharge, which is described as the storage of water *Study on the Impact of Artificial Recharge on Treated Domestic Sewage DOI: http://dx.doi.org/10.5772/intechopen.109868*

**Figure 1.** *Unconfined and confined aquifer systems.*

underground. During periods of water scarcity, the requirement of additional water is been provided as per demand. Artificial groundwater replenishment with treated wastewater is a crucial and necessary practice with several benefits. It helps to avoid groundwater depletion first and foremost. Second, it maintains water in a certain basin or watershed (i.e., the water is not lost to surface water outflow from the watershed or discharge to the ocean). Third, it may save a lot of money when compared to alternative water sources (**Figure 2**) [3].

With recovered water, three methods of groundwater recharge are typically used: subsurface injection into the vadose zone, surface spreading, and direct injection into the aquifer. **Figure 3** illustrates these three ways.

**Figure 2.** *Different types of aquifer recharge [2].*

**Figure 3.** *Different methods in groundwater recharge [4].*
