How does a well work? Is there a finite amount of water in a drinking well? Why is it okay to drink? Do they somehow replenish water or if they dry up that is it?
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A well is basically just a hole in the ground. It’s deep enough that the bottom of the well is below the groundwater table, penetrating the aquifer. An aquifer is a strata of soil, typically sandy porous stuff, that bears groundwater. The sides and bottom of the well are typically porous which allows water to flow from the ground into the cavity of the well. Old wells are typically lined with cobbles or stone, modern wells are typically a pipe with slots cutting into the wall. Construction of the well keep the sand from flowing in but let water flowing into the well. You can bucket the water out or pump it out depending on how sophisticated the design is.
The water in the aquifer is typically finite. But it does get recharged naturally from rain, streams, or some other means. When you pump water out of the well, the water surface in the well dip down lower than the surrounding water surface which causes a gradient. The water will try to equalize this difference by flowing from the ground (which is higher) and into the well (which is lower). Depends on how porous and productive the aquifer is, this flow rate, recharge rate, can range from hundreds of gallon per minute to thousands of gallon per minute.
Lacking recharge or over pumping, the water table will lower and so the water in the well will also lower. At some point the water table is lower than the bottom of the well and you can’t just get water out anymore. The well can be redrilled to deeper depth but that’s not always practical.
Water straight from the ground is raw water. It’s likely cleaner than surface water but it is still raw. Groundwater is considered safer because it basically has to flow through the ground which acts as a sand filter before it gets into the well. This sand filter helps get rid of a lot of non-dissolvable solids, but it doesn’t filter out chemicals, bacteria, and other dissolvable contaminants. It’s recommended to boil the well water to make it safe to drink.
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