rain water is second best to distilled or purified water!, it has or should have an extreemly low EC, unless you have alot of bird shit on the roof! PH is always around 7 to 7.2 , as we always adjust the PH this is irrelevant!
whats more important to remember is tap water has on average 150 additives, that allow the water to be processed and stored in the pipes, believe it or not it contains cyanide in trace elements for anti disentery and other mnasty such things, really the chlorine is one of the least harmfull substances added to tap water!and will almost disolve out in 24 hrs if left to sit [air],
rain water like purified and distilled water does lack some elements that will need to be addressed by using the right nutes! ie calcium! you need nutes made for purified water not tap water!

good luck!


welcome to the world of endless possiblities,,,,,hydroponics