In some areas there are attempts to collect rainwater in cisterns. In general, these cistern waters are harder and contain more total solids than rain. This is due to the accumulation of dirt and dust on the surface of the cisterns. One study shows that in 500 household cisterns, hardness ranged from 35 to 150 ppm. Further, cistern waters often have a high bacterial count and noticeable color. While in many cases the organisms found in cisterns are nonpathogenic, it is advisable to chlorinate this water where it is used for drinking purposes.
Nonpathogenic. A pathogen is any micro-organism or virus that is disease-producing. Hence "nonpathogenic" is a term that refers to the fact that a substance does not contain disease-producing organisms.