Purifying a dirty (by rain) water or rusty water:
Beside settling, sedimenting in a storage tank, a good help is a wonderful material in Thailand easily and cheaply available:
SaanSom (Alum). That is what our fathers used to stop bleeding after shaving.
People in village know about that, they add it to the storage tank for faster settling.
The miraculous flocculating effects even at a strong rusty water I have described in my thread about affordable swimming pool:
https://teakdoor.com/construction-in-...ml#post2860357
How to purify rusty (by iron) water:
https://teakdoor.com/construction-in-...ml#post2853328