Water has such harmful impurities that we can not visualize with our open eyes, and those excrements can not be removed through the boiling process.
Boiling destroys microbes and pathogens but does not eliminate all dangerous impurities such as Arsenic, Cadmium, Lead, Iron, Fluoride and other heavy metals.
The presence of such excrement in water causes harmful diseases, including hepatitis A &B, jaundice, cholera, typhoid and cancer as well.