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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Ground water can be at quite a low level in a lot of places.
Just dig a hole a few metres (a few more feet, i dont know…) down and your hole will start to fill with water soon enough.
Take out a few buckets and soon enough, the level will rise again to “ground water level”
Its ground water so usually not contaminated by much.
The ground is actually quite a decent filtration device.
Just make sure to keep animals from falling into your well (by covering it with a lid)
And of course its all within reason.
No well has water we’d consider extremely clean.
Its usually just “safe enough” but better to boil it first
During long periods of drought, the ground water level may fall and the well may run dry.
If the water level rises, so does the well refill.
But if your local farmers dig a canal to water their crops, the well may run dry more permanently.
Modern wells are generally drilled into bedrock. Rock is porous, even something like granite. So the water moves in underground streams called aquafers through the rock, which filters all of the bad stuff out of the water. Unfortunately, it can also put bad stuff into the water, like various minerals — even arsenic. That’s why people with wells should test their water periodically, to make sure it’s still OK.
The well itself is a hole drilled into the rock bearing the aquafer. It’s about 6-8 inches wide and usually somewhere between 200-800 feet deep. It fills with water, which is pumped out, and can seem ‘infinite’ as long as it’s not pumped out faster than it’s replenished.
However, aquafers aren’t infinite, and too many wells into a single one can deplete it, or slow the rate at which it refills the well.
Typically there is a water table, or a depth where if you were to dig you would hit water. They drill down below that depth and add a pipe to pump the water up.
When it rains the water goes into the ground and fills the well but during drought season it can go empty if more water is used than what the well holds.
(Literally just went through that with a sale of my fathers property. 75′ wasn’t deep enough for the buyer to run 300 gallons to test the septic…)
Wells work using the water underground. The ground is full of little cracks and lets water seep down into it when it rains. Some of this is lost on the surface due to evaporation but some of stays in the ground. Using scientific methods we can see how far below the ground the water is. This is known as the water table. If you dig a hole that goes deeper than the water table, the water, following gravity, will flow into the gap you have just dug. This fills it up the hole and is how wells replenish thier water.
The best example i can give of this is digging holes in the sand at the beach. The water table there is pretty much level with the sea. When you start digging the sand is dry, then it seems to get more ‘wet’ the deeper you go. And when you get below the water level the hole fills with water quickly.
Most wells get their water from aquifers. An aquifer is a layer of rock and soil with water flowing through it. Groundwater drips slowly through the small spaces within rocks, between rocks, and between loose materials such as sand and gravel. New water, such as from rain or melting snow, drips into the ground. The layer of ground just below the surface is a mix of rock, soil, water, and air bubbles. When gravity pulls the water in the ground deep enough, it fills all of the possible pores and cracks, forcing the air bubbles up. At this depth, the ground becomes saturated with water. The boundary between the unsaturated ground and the saturated ground is called the water table. The exact location of the water table depends on how much new water there is, how quickly the water is flowing away, and how permeable the ground is. If you dig a hole into the ground that ends below the water table, the water in the saturated ground is pulled by gravity into the empty space at the bottom of the hole. The hole fills up with water that drips out of the holes in the rocks. A well is simply a hole dug deep enough that it is below the water table, and therefore fills up with water. Old wells used buckets to remove the water from the well, and modern wells use pumps powered by electricity to drive water up. Because the water goes through layers of sand and rock, it is usually clean. But it depends on what kinds of things are in the sand and rock. That’s why well water has to be tested regularly.
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.
I have a well and always wonder if I’m drinking runoff from people’s chemically treated lawns. Are those chemicals filtered out by rocks?
Hi!
There are several things to consider . . .
* A normal suction hand pump has a theoretical limit of 32 feet deep, and a practical limit of about 25 feet deep/ Below this depth you need a “deep well” style of pump which is usually submersed at the bottom of the well.
* Surface water will find a low spot (puddle, pond or lake), but if the soil is porous enough the water will sink (filter) through the soil. Here in Eastern Canada I have send “send point wells” in the basements of homes less than 15 feet below the basement floor.
* Drilled wells (like mine) are often as deep as 200 feet. They have a pump inside the well. It pushes water up the pipe that goes deep into the ground.
* They talk about the flow rate of a well. This is the amount that can be pumped out of the well without making the well go dry. Think of it as the rate water flows into the well.
>Why is it OK to drink?
The water in a deep well has been filtered through the sand, gravel, rocks and soil so it is generally clear. Surface water (ponds, streams, puddles) often has bacteria in it. [read PDF here](https://www.des.nh.gov/sites/g/files/ehbemt341/files/documents/2020-01/bb-14.pdf) These bacteria require oxygen, and do not tend to be in deep wells.
People get their wells tested, and not all wells produce good water.
I lived in a rural community where many wells had uranium in the water. My current well has calcium, manganese and iron. It is very healthy, but had on washers and dishwashers.
On top of what everyone else wrote, groundwater is from the sky and runoff, percolated through a natural filtration system (soil, Quaternary deposits, permeable bedrock – i.e. sandstone, siltstone, chalk, limestone, etc.), and extracted from the ground through a relatively clean hole. Whereas surface water (lakes, rivers, ponds), are all mostly contaminated with mining spoil if you’re near ongoing or historical mining operations (dangerous levels of heavy metals near running water). This is in most UK rivers downstream, especially the North of England.
Why is groundwater not filled with heavy metals or other toxic/biologically dangerous substances? Sometimes it is. So please check your wells with testing kits! But often than not, if there has been ground investigation before the creation of the well, and if the geology is harmless (mostly limestone, chalks, unmetamorphosed sandstones) it should be fine and cleaner than dirty surface water.
Any Qs, feel free to ask. Ex-geotechnical engineer w/ a geology degree. 👋
Sister used well water for her house. Every water-using appliance was colored orange from the high mineral content. Bathtub was brown.
Drinking well water tasted like drinking dirt.
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