Plant sippers work similarly to how an aquifer works.
A plant sipper is an empty plastic tank or reservoir that can hold water and has a long hollow tube attached to it so water can be added to the tank. They are used to reduce the amount of water needed to keep plants alive.
The tank is placed in a planter below the area that the plants' roots will be. As the plants establish themselves, their roots will extend towards the tank of water. And then, by capillary action, the plant will draw water when the plant needs it.
The long tube connected to the tank will need to be just above the top of the soil level to allow for water to be easily added to the tank. The tube has a float inside that rises when the tank is full of water and lowers as the water is used.
Plant sippers, or self-watering reservoirs, save on the overall amount of water required for growth and, therefore, decreases watering frequency.