How does water get filtered while passing through sand, charcoal, etc.?

Question

How does water get filtered while passing through sand, charcoal, etc.?

In: 3473

Answer 1

While most answer have focussed on mechanical filtration: aka sieving and physical stopping of bad particles, i would also like to point out there is a biological component:

Bacteria that stick to the sand/… particles eat certain bad molecules and break them down to less damaging components.