For our purposes of DIYing a water filter system, you'll want to use more natural materials like sand and gravel or small rocks.

Sand filters are commonly used for keeping your swimming pool’s water clean, but over time the pool filter sand can become dirty and contaminated, which affects how well the filter can function ...

One group, from Pennsylvania State University, is developing a special, antibacterial Moringa sand that it hopes people could easily make at home and use to filter their own water.