Raining Water for the Use of Boiler

For water cooling, it is possible but for the boiler which I am not sure because the water content in the boiler must be always same and exactly throughout the year, so we do not know what kind the water content in the rain water especially there are some pollution in the rain water which are is not stable for boiler. Or unless special treatment filtration can be apply to boiler and generation of steam.

Or unless I am all wrong about this. Please tell me if I am wrong in some area. :-)

I general, feed water for a boiler should be demineralized. Rainwater collects dust, not only while forming and falling, but from the surfaces upon which it falls. The collection of rainwater is a very good idea since fresh, potable water for animal and food preparation will be our next major crisis. As for process water, regardless of how it is obtained, it will always need some sort of treatment before it can be used. Even water for irrigation needs to be cleaned of some possible contaminants such as heavy metals, etc.