That is the "old tech"
Now the BioSand filter.
Source water can not contain chlorine, soap or salt water as they will stop the bio-filtration process.
The BioSand Filter
This PDF is a MUST READ!
It takes 5‐10 days for the biological layer to reach full maturity and effectiveness. During this time, the filter will become increasingly effective. Post filtering chlorination provides safe water during the period of time it takes for the biological
layer to form.
A PDF "manual" on water safety, and excellent read with lots of basic info.
A treasure of PDF files on how this type of filter is built and works.