I don’t understand how do wells work. Like, I’ve seen a lot of wells made of stone, so, if you dig a huge hole in the ground, how does water come inside the well? Like, I’ve seen a lot of movies where someone gets stuck in a well or something, and there’s always a rock bottom. So, how does water get inside the well?
In: Engineering
Groundwater that you pump out of wells rarely occurs like an “underground river”. Sometimes solid rock is fractured and water moves through these fractures. But the most common groundwater is found between the the grains of sediment deposited by water or wind. This also can even occur between the grains of rock like sandstone. It is a bit like the water that has been sucked up by a sponge.
If you drill or dig a well down below the water table to where the space between the grains is completely filled by water, the water will flow into the well. But the trick is that you have to keep the sediment from collapsing in and filling the hole, unless the well is in solid rock. So you use something like a metal pipe or a wall of rocks to keep the hole open.
The trick is that you also need to let the water flow into the well. Leaving the hole open at the bottom isn’t usually good enough because there isn’t enough surface area for water to flow in and you won’t be able to pump much water. If you dig a well and line it with stone blocks the water can flow in through the cracks but it will still keep the dirt out (mostly). Modern drilled wells use a “well screen” – often a metal section with tiny slots to keep the sediments out but allow water to seep in. You can provide a lot more open area this way than by just leaving the hole open at the bottom.
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