No. Rainwater is pure. Rooftops are dirty, but filters can easily remove contaminants. We have installed systems where people use ONLY rainwater for drinking year round. Venerable institutions such as the Chaudhary Group, TEWA, Butwal Power Company, GEMS school and Jyoti Group have installed rainwater harvesting and use it for all the same uses they use municipal or tanker water for. Simple filtration or chlorination can make rainwater fit for drinking.