If you dig 2 holes near a river one close to the river and the other further back on the river bank. The first fills with water then it travels through the sand into the second hole and it will be filtered a lot. Don't remember the name of the technique
If you dig 2 holes near a river one close to the river and the other further back on the river bank. The first fills with water then it travels through the sand into the second hole and it will be filtered a lot. Don't remember the name of the technique