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More than 45 million people are served by 13 million private water wells in the United States. Understanding the basics of how your well provides safe drinking water to your home is important for performing maintenance steps properly, as well as tackling any problems as they arise.
Water flows naturally in a groundwater system based on the hydraulic pressure put on the system. The flow can be horizontal though a geologic unit or vertical through several different geologic units, or sometimes some of both. Figure 1 shows how water moves naturally though a groundwater system. The thin layers with horizontal dashes in Figure 1 represent confining layers (aquitards) that separate the aquifers shown in blue. As you can see on the figure, because the high point of the water table is near the left edge, water is flowing downward from the high point toward areas of lower water levels in both directions (lower levels = less pressure).
Figure 1: Adapted from Minnesota Department of Health
When your well pump kicks on and starts drawing water from your well, the water level in your well drops, creating a water pressure difference between the water in your well and the water in the surrounding aquifer. Water flows into your well to replenish the withdrawn water. How fast water can move to your well affects how much the water level drops in your well. This drop is called the drawdown in your well. As water flows into your well, it lowers the water level in the surrounding aquifer as well, creating a cone-shaped area of lower water levels around your well. This is called the cone of depression.
The water level in your well can also change over time. In some areas, well owners have never had a pump in their well because their well flows naturally. In other areas, heavy rains or flooding can cause wells to start flowing. Conversely, drought can reduce recharge to the aquifer, which reduces the pressure head, which can cause some flowing wells to stop flowing. Understanding that the water level in your well can change because of natural factors will help you understand how your well works and if there are any risks of contamination.
Basic Components of Your Well System
Your well may be where your water comes from, but without the mechanical system to convey the water to your house, store it, and provide the pressure so it will flow, your well would be useless. Figure 2 is a typical well and water system for a home. In this example, the well has a screen, so it’s a well finished in a sand and gravel aquifer. The pump is in the well just above the screen. The pump lifts water up a pipe (drop pipe) to the pitless unit or pitless adapter, where it elbows horizontally and goes into the house through the discharge pipe. From there water goes into the pressure tank, or straight into the line to your faucets, shower, or dishwasher (if it’s a period of heavy water demand that kicked on your pump).
Figure 2: Adapted from Minnesota Department of Health
Well Pump: When a pump is installed in or at a well, it is sized for the particular situation it is being used for, as well as the characteristics of the well. Some of the factors considered include well size, maximum anticipated use, water level, amount of piping, number of sources (# of faucets, fixtures, etc.), well yield, and pressure needed in the home. You want to have a large enough pump to do the job, but if you have too big a pump, it will waste energy.
Pitless Adapter: A pitless adapter is a fitting for a well that eliminates the need for a well pit. It goes through a hole in your well casing at a depth below the frost line that provides a sealed connection between the drop pipe in your well and the discharge line going from the well to your house. Many years ago, to prevent freezing pipes in the winter, wells were completed below land surface at a depth below the frost line.
Note on Well Pits: Well pits are dangerous. They can hold water that can contaminate a well; they are a safety hazard for people, livestock, and moving equipment; and they can collect dangerous gases that could incapacitate someone getting into the pit. In fact, if your well is in a pit, and many still are, it’s in your best interest to have a contractor extend your well to above land surface and use a pitless adapter to maintain the discharge line connection to your well.
Pressure Tank: The water entering your home is pumped into a pressure tank. Pressure tanks operate by maintaining a range of pressure in the tank to force water out into the line when a faucet or other source is opened. In addition to helping keep the water under pressure, pressure tanks also provide water storage. Water in the tank can be used when the pump is not running and in times of high demand to help the pump keep up.
Additional Resources:
What is a cone of depression? (video). 2021. University of Minnesota Water Resources.
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