eli5: how do water filters work?
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Activated carbon filters work by having tons of little holes and twisted pathways through a pack of carbon molecules. Common impurities in drinking water get trapped in the pathways and/or get stuck to the carbon, while the water can pass through (although slowly). The end result is a dirty filter, but clean(ish) water.
By passing water through materials that will only fit certain sizes of things through.
It sounds relatively simple and at a basic level is. Though there are different types from basic ones to fill reverse osmosis systems used in desalination systems.
There can be different levels of them at a basic level, [like passing through coarse filters to remove dirt and debris, increasingly smaller material ](https://content-instructables-com.cdn.ampproject.org/i/s/content.instructables.com/ORIG/FL8/HFR1/IY3CSVIS/FL8HFR1IY3CSVIS.jpg?auto=webp&fit=bounds&frame=1&auto=webp&frame=1&height=300). Then maybe charcoal to absorb off flavor components that still got through.
Note, a filter like this ***does not*** remove waterborne pathogens. It still needs to be boiled or treated with chemicals like iodine or chlorine to kill those.
At higher levels more complex systems live reverse osmosis will have molecule sized screens that require high pressures to force water through but this requires higher energy to build that pressure. Which is one of the many challenges with just desalinating a ocean water to solve droughts, it’s expensive, energy intensive and ecologically tricky. It’s worth it to stop people from dehydrating but for large scale uses it gets more expensive.
On a larger scale, think of a river or stream polluted with trash and debris. If you want to filter out the trash you can take a net and place it across a point in the river. The trash will be too big to pass through the holes in the net but the water can still pass through. What happens is the trash collects at the point where the net is and the trashless water passes through.
This is basically what a water filter does but on a smaller scale. You essentially have a barrier that allows water molecules to pass through but is too small to allow microorganisms, dirt, debris, and other harmful or undesirable particles to pass through.
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